BACKGROUND: Management of respiratory motion during radiation therapy is essential for accurate dose delivery and minimizing the risk to organs. In diagnostic imaging, respiratory monitoring is required for confirmation of breath-hold and four-dimensional computed tomography (CT) reconstruction. Although respiratory monitoring systems are widely used in radiation therapy, they are not often used for diagnostic imaging, where they could improve image quality. PURPOSE: The purpose of this study was to use a millimeter-wave sensor (MWS) to noninvasively visualize respiratory motion, confirm breath-holding, and explore the potential for clinical implementation of an MWS in diagnostic x-ray imaging, CT, and radiation therapy. METHODS: A 24 GHz microMWS was used in this study. The MWS directionality was determined using a radio-wave dark-box system. An antenna directionality test evaluated the effective azimuthal and elevational beamwidths. Respiratory waveforms were detected by optimizing the fast Fourier transform threshold and the cutoff frequencies of the bandpass filter. To confirm the reproducibility of the MWS, the detected waveforms were compared with those of a respiratory motion phantom (QUASAR), the amplitude of motion of which could be controlled. The time from valley to peak of the waveforms obtained by normalized MWS and the QUASAR were compared. The MWS was used to acquire respiratory waveforms of 20 healthy volunteers (including an infant and a child) in geometries adopted during chest CT (supine position; anteroposterior view; source-to-surface distance, 400 mm) and chest x-ray imaging (standing position; posteroanterior view; source-to-surface distance, 1800 mm). RESULTS: The effective azimuthal and elevational beamwidths of the MWS were approximately ± 20° and ± 40°, respectively. By optimizing the acquisition parameters (high-sensitivity setting; with noise cancelling; frequency range, 10-20 min-1), the waveforms detected using the MWS approximately matched those of the respiratory motion phantom at all amplitudes. The MWS was also used to confirm breath-holding in 18 volunteers in both supine (anteroposterior view) and standing (posteroanterior view) positions. In addition, for an infant and a child who were unable to follow the instruction to stop breathing, a visual count of their inhalations matched the number of respiratory cycles measured using the MWS. CONCLUSION: The 24 GHz MWS successfully monitored respiratory motion and breath-holding during radiographic and CT imaging. With effective directionality and stability, this system holds promise for clinical management of respiratory motion during diagnostic imaging and radiation therapy.

BACKGROUND/AIM: This study aimed to clarify the feasibility of creating coplanar single-isocenter volumetric modulated arc therapy (SI-VMAT) with a Halcyon using a knowledge-based planning system based on non-coplanar plans for treating multiple brain metastases. PATIENTS AND METHODS: A knowledge-based RapidPlan (RP) planning model was built using 32 TrueBeam SI-VMAT plans including one full arc and three non-coplanar partial arcs. To confirm its applicability across different beam geometries using the Halcyon system, the model was validated on the basis of the root-mean-square error (RSME), deviation rate, and absolute differences between estimated and actual dose-volume histograms (DVHs). Dosimetric performance of TrueBeam and Halcyon plans was then compared for 10 patients. RESULTS: The average RSME values for the Halcyon and TrueBeam plans were 0.75±0.40 Gy and 0.46±0.28 Gy, respectively (p<0.05). Using the model for Halcyon plan creation, deviations from the estimated DVH boundaries were mainly observed in the low-dose region (<9 Gy), while the actual DVH closely aligned with the estimated DVH in the intermediate- and higher-dose regions. For comparison of dosimetric performance, statistically significant differences were found in the gradient index, conformity index, and normal brain volumes receiving ≥12 Gy, ≥18 Gy, and ≥27 Gy. However, these differences were deemed clinically negligible, with less than 1% disparity in the above doses to the normal brain. CONCLUSION: The RP model can effectively predict doses for Halcyon, regardless of different beam configurations. Coplanar SI-VMAT with Halcyon can feasibly be used in clinical applications, such as the treatment of multiple brain metastases.

This study examined the characteristics of the broad model (KBPbroad) through a complete open-loop evaluation of volumetric modulated arc therapy (VMAT) plans for prostate cancer in 30 patients at two institutions. KBPbroad, trained using 561 prostate cancer VMAT plans from five institutions with different treatment protocols, was shared with two institutions. The institutions were not involved in the creation of KBPbroad. Plan created with KBPbroad were compared with clinical plans (CPs) and plans created using a single-institution model at each institution (KBPonsite). KBPbroad maintained the target coverage of CPs while meeting dose limits across varied settings at each institution. At institution X, KBPbroad provided 40, 60, and 70 Gy (V40Gy, V60Gy, and V70Gy, respectively) to 30.8% ± 9.9%, 15.3% ± 8.5%, and 9.0% ± 6.4% of the volume at the rectal wall, respectively, which were significantly smaller than those provided by KBPonsite and CPs. At institution Y, compared with CPs, KBPbroad provided significantly greater V50Gy, V70Gy, dose to 2% of the volume (D2%) at the rectum, and D2% at the bladder but significantly lower V50Gy and V70Gy at the bladder, in addition to superior dose homogeneity and conformality at the planning target volume. Our complete open-loop evaluation of VMAT plans for prostate cancer at two institutions demonstrated the clinical effectiveness of KBPbroad at institutions producing plans with insufficient reductions in OAR doses. Thus, the quality of KBPbroad plans is likely greater than that of KBPonsite plans and CPs.

BACKGROUND/AIM: This study aimed to determine whether a knowledge-based planning model incorporating treatment plans with multiple collimator angles (Multi-coll. model) provides superior estimation accuracy and plan quality for a range of collimator angles compared with a typical institutional model (Inst. model). MATERIALS AND METHODS: Five institutions using volumetric modulated arc therapy for prostate cancer participated in the study. The Inst. model comprised plans using a fixed collimator angle, whereas the Multi-coll. model registered plans using single arcs and collimator angles of 10°, 30°, 50°, and 70°. The coefficient of determination and mean squared error were calculated, and the estimation accuracy and dosimetric results for three validation cases at each institution were compared for each model. Dosimetric parameters included volumes receiving at least 20%, 50%, and 90% of the prescription dose (V20, V50, and V90, respectively) at each collimator angle. RESULTS: The Multi-coll. model yielded a higher coefficient of determination and lower mean squared error than the Inst. model, although overfitting of data was a concern at two institutions. The mean absolute errors between estimated and calculated values were (Inst. model vs. Multi-coll. model): 4.41% vs. 2.60% (V20), 4.03% vs. 2.27% (V50), and 2.07% vs. 1.09% (V90) for the rectum; 3.48% vs. 3.42% (V20), 2.24% vs. 3.65% (V50), and 1.11% vs. 0.73% (V90) for the bladder. The Multi-coll. model exhibited a lower rectal and vesical V20 than the Inst. CONCLUSION: The Multi-coll. model had a greater estimation accuracy and slightly higher plan quality than the Inst.

PURPOSE: The clinically accepted planning target volume margin for radiation therapy to the paraortic nodal region in cervical cancer patients is 5 mm. However, the comprehensive alignment and variability from the pelvic bone to all lumbar vertebrae are undetermined. This study aims to quantify the residual setup errors between the pelvic bone and lumbar vertebrae and determine the optimal correction strategy for patients with cervical cancer. MATERIALS AND METHODS: Fifteen patients underwent pretreatment mega-voltage computed tomography scans (375 total fractions). Residual setup errors and required margins for each lumbar vertebra were calculated based on registrations accounting for pelvic rotation and translation. RESULTS: The systematic residual errors (1 SD) at L1, L2, L3, L4, and L5 using pelvic bone registration were 6.5, 4.9, 3.1, 1.5, and 0.6 mm in the anterior-posterior (AP) direction, 3.1, 2.3, 1.4, 0.6, and 0.3 mm in the right-left direction, and 2.7, 2.2, 1.7, 1.0, and 0.5 mm in the superior-inferior direction, respectively. The residual setup errors were the largest in the AP direction. Registration based on the pelvic bone required margins in the AP direction of 16.0, 12.1, 7.7, 3.6, and 1.3 mm for L1, L2, L3, L4, and L5, respectively, whereas registration based on L3 required margins of 8.8, 4.8, 4.4, 7.1, and 7.7 mm for L1, L2, L4, L5, and pelvic bone, respectively. CONCLUSIONS: Considerable local setup variability was found in patients with cervical cancer. After reviewing the corrective strategies, we determined that L3-based registration effectively minimized the required margins.

Radiation therapy with X-rays for skin cancer uses a bolus to increase the surface dose. Commercial gel sheet boluses adhere poorly to the patient's body because of surface irregularities. This causes an air gap and reduces the surface dose. We have developed a novel shapeable bolus (HM bolus; Hayakawa Rubber Co., Ltd., Hiroshima, Japan), and we describe the first clinical application of this bolus here. The case was an 82-year-old male with a facial cutaneous squamous cell carcinoma. The postoperative radiotherapy plan using the HM bolus provided a more uniform dose to the target compared with a plan without the HM bolus. The HM bolus adhered stably to the patient's skin, and there were no issues with its clinical use.

The present study aimed to evaluate whether an adapted plan with Ethos™ could be used for pharyngeal cancer. Ten patients with pharyngeal cancer who underwent chemoradiotherapy with available daily cone-beam computed tomography (CBCT) data were included. Simulated treatments were generated on the Ethos™ treatment emulator using CBCTs every four to five fractions for two plans: adapted and scheduled. The simulated treatments were divided into three groups: early (first-second week), middle (third-fourth week), and late (fifth-seventh week) periods. Dose-volume histogram parameters were compared for each period between the adapted and scheduled plans in terms of the planning target volume (PTV) (D98%, D95%, D50% and D2%), spinal cord (Dmax and D1cc), brainstem (Dmax) and ipsilateral and contralateral parotid glands (Dmedian and Dmean). The PTV D98%, D95% and D2% of the adapted plan were significantly higher than those of the scheduled plans in all periods, except for D98% in the late period. The adapted plan significantly reduced the spinal cord Dmax and D1cc compared with the scheduled plan in all periods. Ipsilateral and contralateral parotid glands Dmean of the adapted plan were lower than those of scheduled plan in the late period. In conclusion, the present study revealed that the adapted plans could maintain PTV coverage while reducing the doses to organs at risk in each period compared with scheduled plans.

OBJECTIVE: The purpose of this study is to determine the dose reduction of different shielding materials at various distances from a 177Lu photon radiation source. METHODS: Two protective aprons with lead equivalent thicknesses of 0.25 mm and 0.35 mm and tungsten-containing rubber (TCR) were used as shielding materials. A vial containing 177Lu was sealed in a lead container so that a narrow beam went out through a 3 mm-diameter hole. The dose rate was measured at distances of 0, 10, 50, 100, and 200 cm from the source using a NaI scintillation survey meter to obtain the rate of dose reduction. TCR was tested with thicknesses ranging from 0.3 to 1.0 mm at 0.1 mm intervals and from 1.0 to 4.0 mm at 0.5 mm intervals. RESULTS: At distances of 0, 10, 50, 100, and 200 cm, the dose reduction for the lead equivalent thickness of 0.25 mm were 32.7%, 54.5%, 93.1%, 97.9%, and 99.6%, respectively; and for the lead equivalent thickness of 0.35 mm were 53.4%, 70.6%, 95.6%, 98.9%, and 99.6%, respectively. Without any shielding, the dose rate decreased by 34.4% at 10 cm and by 88.8% at 50 cm from the radiation source. The dose reduction for the TCR thickness of 3.5 mm was 89.8% at 0 cm and 93.3% at 10 cm. The TCR thickness of 0.4 mm provided a dose reduction comparable to or greater than that of the 0.25 mm lead equivalent, whereas the TCR thickness of 1.0 mm or greater provided a dose reduction comparable to that of the 0.35 mm lead equivalent. CONCLUSIONS: Achieving a reduction of 95% or more requires the 0.25 mm lead equivalent for a distance of 100 cm, the 0.35 mm lead equivalent for 50 cm, the TCR thickness of 0.3 mm for 100 cm, or the TCR thickness of 0.9 mm for 50 cm. Without wearing a protective apron, a reduction of approximately 95% is observed at distances greater than 100 cm. These findings would be useful for medical staff engaging in related activities.

PURPOSE: To evaluate whether knowledge-based volumetric modulated arc therapy plans for prostate cancer with a multi-institution model (broad model) are clinically useful and effective as a standardization method. METHODS: A knowledge-based planning (KBP) model was trained with 561 prostate VMAT plans from five institutions with different contouring and planning policies. Five clinical plans at each institution were reoptimized with the broad and single institution model, and the dosimetric parameters and relationship between Dmean and the overlapping volume (rectum or bladder and target) were compared. RESULTS: The differences between the broad and single institution models in the dosimetric parameters for V50, V80, V90, and Dmean were: rectum; 9.5% ± 10.3%, 3.3% ± 1.5%, 1.7% ± 1.6%, and 3.6% ± 3.6%, (p < 0.001), bladder; 8.7% ± 12.8%, 1.5% ± 2.6%, 0.7% ± 2.4%, and 2.7% ± 4.6% (p < 0.02), respectively. The differences between the broad model and clinical plans were: rectum; 2.4% ± 4.6%, 1.7% ± 1.7%, 0.7% ± 2.4%, and 1.5% ± 2.0%, (p = 0.004, 0.015, 0.112, and 0.009) bladder; 2.9% ± 5.8%, 1.6% ± 1.9%, 0.9% ± 1.7%, and 1.1% ± 4.8%, (p < 0.018), respectively. Positive values indicate that the broad model has a lower value. Strong correlations were observed (p < 0.001) in the relationship between Dmean and the rectal and bladder volume overlapping with the target in the broad model (R = 0.815 and 0.891, respectively). The broad model had the smallest R2 of the three plans. CONCLUSIONS: KBP with the broad model is clinically effective and applicable as a standardization method at multiple institutions.

Abstract Objective. The purpose of this study was to develop a new bolus (HM bolus), with tissue equivalence, transparency, reusability, and free shaping at approximately 40 °C for excellent adhesion, and to evaluate the feasibility of clinically using this bolus as an ideal bolus. Approach. We summarized the advantages and disadvantages of existing boluses. To evaluate dose characteristics, a vinyl gel sheet bolus (Gel bolus) and HM bolus placed on a water-equivalent phantom were used to obtain the percentage depth dose (PDD) of electron (6 MeV, 9 MeV) and photon (4 MV, 6 MV) beams. The average dose difference of the HM bolus and Gel bolus was calculated. The Gel bolus, a soft rubber bolus (SR bolus), and HM bolus were placed in adherence to a pelvic phantom. CT images taken after shaping and 1, 2, and 3 weeks after shaping were used to evaluate the adhesion and reproducibility using air gap and dice similarity coefficient (DSC). Main results. The average dose difference for electron beams was 0.16% ± 0.79% and photon beams was 0.06% ± 0.34%, both within 1% of the PDD results. The HM bolus showed the same build-up effect and dose characteristics as the Gel bolus. The mean air gap values for the Gel bolus, SR bolus, and HM bolus were 96.02 ± 43.77 cm³, 34.93 ± 21.44 cm³, and 4.40 ± 1.50 cm³, respectively. The mean DSC values compared to initial images for the Gel bolus, SR bolus, and HM bolus were 0.363 ± 0.035, 0.556 ± 0.042, and 0.837 ± 0.018, respectively. Excellent adhesion was observed in the CT simulation and during the treatment period. Significance. The HM bolus has unique features, such as tissue equivalence, transparency, reusability, and free shaping for excellent adhesion, and is thus an ideal bolus for use in clinical cases.

This study aims to determine the feasibility of using a new O-ring linear accelerator (Halcyon, Varian Medical Systems, CA, USA) to perform treatment planning using volumetric modulated arc therapy (VMAT) for craniospinal irradiation (CSI). A 20-year-old male patient with leukemia was selected. The planning target volume (PTV) was contoured to include the entire contents of the brain and spinal canal. The PTV margin was 10 mm applied to the clinical target volume (CTV). VMAT (RapidArc, Varian Medical Systems, CA, USA) planning was performed using four isocenter with five arcs, two full rotation arcs to cover the brain and upper part of the spinal cord, and one full rotation arc for the lower part of the spinal cord. The plan was created using the auto-feathering photon optimizer calculation of the planning system. The conformity index (CI) and heterogeneity index (HI) as well as dose-volume histograms of organs at risk (OAR) were evaluated. The patient position of ±3.0 mm in the craniocaudal direction was moved in to simulate the effect of treatment inaccuracy. The total treatment time was also measured. The CI and HI were 1.09 and 8.44, respectively. The mean dose (PTV) was 105.5%, and the mean dose (OARs) was lower than the planning dose constraints. Simulations with a patient position shift of ±3.0 mm resulted in an error of less than ±10.0% of the planned dose to the spinal cord. The total treatment time was within 15 minutes. VMAT planning for CSI with Halcyon achieved high conformality, uniform dose distribution, low dose to the surrounding normal tissues, and reduced treatment time.

Abstract This study aims to measure the shielding effect of a novel tungsten rubber sheet (TRS) on the exposure of male gonads to ionizing radiation during upper abdominal and abdominal plus pelvic computed tomography (CT) examinations. The air kerma at the gonad with and without shielding was measured using an anthropomorphic body phantom. Gonads were shielded using: (1) 360° wrap with TRS (0.5-mm thick) and (2) 180° wrap with TRS. The air kerma at a position of male gonads in a pelvic scan was 21.8 mGy, even when the gonads were in the off-axis range. The TRS reduced the dose to the male gonads in abdominal plus pelvic CT examinations by 61% and 38% for the 360° and 180° TRS wrap, respectively.

Background Coronavirus disease 2019 and other viruses are transmissible by aerosols and droplets from infected persons. This study aimed to develop a portable device that can trap droplets and deactivate viruses, and verify whether the device in an enclosed room can suction droplets and sanitize them using a filter and an ultraviolet-C (UVC) light-emitting diode. Materials and methods The portable device was evaluated by placing it 50 cm away from the droplet initiation point. A particle image velocimetry laser dispersed into a sheet form was used to visualize the droplets splashed on the irradiated sagittal plane and captured using a charge-coupled device camera at 60 frames per second. The images were overlaid and calculated to determine the percentage of the droplets beyond the portable device. Droplets with a particle size larger than 50 µm that dispersed and were deposited more than 100 cm away were measured using a water-sensitive paper. The effect of UVC sanitization on viruses captured by a high-efficiency particulate air (HEPA) filter was determined using a plaque assay. Results The percentage of droplets was 13.4% and 1.1% with the portable device OFF and ON, respectively, indicating a 91.8% reduction. The deposited droplets were 86 pixels and 26 pixels with the portable device OFF and ON, respectively, indicating a 68.7% reduction. The UVC deactivated more than 99% of the viruses on the HEPA filter surface in 5 minutes. Conclusions Our novel portable device can suck and fall the dispersed droplets, and an active virus was not observed on the exhaust side.

To clarify the dosimetric characteristics of a real-time variable shape rubber-containing tungsten (STR) bolus in a clinical plan and investigate the efficacy of the STR bolus in photon radiotherapy for keloids and other superficial tumors. A 5 mm gel bolus or 1 mm STR bolus was placed on a solid water phantom. Tangential irradiation was performed using a TomoTherapy Radixact-X9 and 6 MV X-ray flattening-filter-free beam, and the surface dose was measured with radiochromic film. Clinical-like plans (TomoDirect; TD and TomoHelical; TH) were applied with the same geometry and the dose distributions were measured. The increase in surface dose by the build-up effect and backscatter was 37.7% and 8.0% for the gel bolus, and 40.5% and 26.4% for the STR bolus, respectively. In the TD and TH plans, the increase in surface dose was 27.4% and 48.3% for the gel bolus, and 39.0% and 63.2% for the STR bolus. Similary, changes in the sagittal plane dose were - 3.9% and 6.1% for the gel bolus, and - 6.3% and 6.9% for the STR bolus. The STR bolus effectively increased the surface dose by the build-up effect and backscatter in photon radiotherapy for keloids and other superficial tumors.

OBJECTIVE: Dosimetric potential of knowledge-based RapidPlan planning model trained with HyperArc plans (Model-HA) for brain metastases has not been reported. We developed a Model-HA and compared its performance with that of clinical volumetric modulated arc therapy (VMAT) plans. METHODS: From 67 clinical stereotactic radiosurgery (SRS) HyperArc plans for brain metastases, 47 plans were used to build and train a Model-HA. The other 20 clinical HyperArc plans were recalculated in RapidPlan system with Model-HA. The model performance was validated with the 20 plans by comparing dosimetric parameters for normal brain tissue between clinical plans and model-generated plans. The 20 clinical conventional VMAT-based SRS or stereotactic radiotherapy plans (CL-VMAT) were reoptimized with Model-HA (RP) and HyperArc system (HA), respectively. The dosimetric parameters were compared among three plans (CL-VMAT vs. RP vs. HA) in terms of planning target volume (PTV), normal brain excluding PTVs (Brain - PTV), brainstem, chiasm, and both optic nerves. RESULTS: In model validation, the optimization performance of Model-HA was comparable to that of HyperArc system. In comparison to CL-VMAT, there were no significant differences among three plans with respect to PTV coverage (p > 0.17) and maximum dose for brainstem, chiasm, and optic nerves (p > 0.40). RP provided significantly lower V20 Gy , V12 Gy , and V4 Gy for Brain - PTV than CL-VMAT (p < 0.01). CONCLUSION: The Model-HA has the potential to significantly reduce the normal brain dose of the original VMAT plans for brain metastases.

BACKGROUND/AIM: This study evaluated the impact of knowledge-based plan (KBP) model improvement on plan complexity and delivery accuracy in volumetric modulated arc therapy (VMAT) for prostate cancer at multiple institutions. MATERIALS AND METHODS: Five institutions created the first KBP model before April 2017 and subsequently devised a new model (second model) based on feedback from the first KBP and the efforts of planners after April 2019. The dose-volume histogram (DVH) parameters were validated for two prostate cancer cases between the first and second KBPs. Plan complexity metrics, of the modulation complexity score for VMAT (MCSv), closed leaf score (CLS), small aperture score (SAS), and leaf travel (LT), were compared. The delivery accuracy metrics of γ pass rate and point dose discrepancy (plan vs. measurement) at isocenter were also compared. RESULTS: There were no significant differences in DVH parameters between the KBPs. Conversely, V50% of the rectum and bladder was reduced in 6/10 and 8/10 patients, respectively, and these variations were also converged from the first KBP to the second KBP. The mean±1SDs of MCSv, CLS, SAS20mm, and LT (first KBP vs. second KBP) were 0.27±0.033 vs. 0.26±0.044, 0.062±0.032 vs. 0.14±0.091, 0.59±0.048 vs. 0.70±0.14, and 411.91±32.08 mm vs. 548.33±127.50 mm, respectively. The delivery accuracy did not differ, whereas MCSv was moderately correlated with the point dose discrepancy. CONCLUSION: Multi-leaf collimator motion could be more complex with KBP model improvement, which had the potential to deteriorate the delivery accuracy.

Independent monitor unit verification (MUV) methods for the dynamic beam-flattening (DBF) technique have not been established. The purpose of this study was to clarify whether MU values for the DBF technique can be calculated using in-air and in-water output ratios (Sc and Scp ). Sc and Scp were measured in the DBF mode, and the phantom scatter factor (Sp ) was calculated. The difference between calculated and planned MUs with square and rectangle fields and clinical plans for different treatment sites was also evaluated. Sc values for the 4 × 4 to 24 × 24 cm2 fields of the distal multi-leaf collimator (MLC) layer at 2-cm intervals were 0.887, 0.815, 0.715, 0.716, 0.611, 0.612, 0.511, 0.373, 0.374, 0.375, and 0.374, respectively. No collimator exchange effect was observed. Sc also depends slightly on the field size of the distal MLC layer. If the distal-MLC-layered field size was less than 20% of the corresponding MLC sequence size in the proximal MLC layer, Sc was affected by >1%, which was compensated using a correction factor (CF). Sp increased as the field sizes of the MLC sequence and distal MLC leaves increased. MUs calculated using measured Sc , Sp , and CF for square and rectangle fields agreed with planned MUs within ±1.2%. A larger difference (-1.5%) between calculated and planned MUs was observed for clinical plans, whereas differences in MUs were within 2 MU for most fields (56 out of 64 fields). MU calculation for the DBF technique can be performed with Sc , Sp , and CF for independent MUV.

PURPOSE: To determine the thickness of a soft variable shape tungsten rubber (STR) as a lung compensating filter in total body irradiation. METHODS: A tough water (TW) phantom and tough lung (TL) phantom were used as water and lung-equivalent phantoms. The TW with a thickness of 3 cm simulating the thoracic wall was used (upper layer). The TW or TL with a thickness from 1 to 15 cm (1 cm increments) was placed beneath the upper layer (middle layer). The TW with a thickness of 5 cm simulating the mediastinum was placed beneath the middle layer (lower layer), and a farmer ionization chamber was placed beneath this layer. The relative doses of a 10 MV X-rays were then measured. The TL was compensated in 1 mm increments from 1 to 11 mm of the STR, and the thickness of the STR at the same dose of TW (water equivalent) was obtained. RESULTS: The compensating ability of STR increased as the thickness of the TL increased, and an STR with a thickness of 1 mm reduced the dose by 2%-4%, depending on the thickness of lung. The STR thickness as an equivalent dose of TW per cm of TL was approximately linear, and the thickness was 0.62 mm/cm of TL. CONCLUSION: The STR can be used as a lung compensating filter for a water equivalent dose with 0.62 mm of STR per cm of lung.

We established a multi-institution model (big model) of knowledge-based treatment planning with over 500 treatment plans from five institutions in volumetric modulated arc therapy (VMAT) for prostate cancer. This study aimed to clarify the efficacy of using a large number of registered treatment plans for sharing the big model. The big model was created with 561 clinically approved VMAT plans for prostate cancer from five institutions (A: 150, B: 153, C: 49, D: 60, and E: 149) with different planning strategies. The dosimetric parameters of planning target volume (PTV), rectum, and bladder for two validation VMAT plans generated with the big model were compared with those from each institutional model (single-institution model). The goodness-of-fit of regression lines (R2 and χ2 values) and ratios of the outliers of Cook's distance (CD) > 4.0, modified Z-score (mZ) > 3.5, studentized residual (SR) > 3.0, and areal difference of estimate (dA) > 3.0 for regression scatter plots in the big model and single-institution model were also evaluated. The mean ± standard deviation (SD) of dosimetric parameters were as follows (big model vs. single-institution model): 79.0 ± 1.6 vs. 78.7 ± 0.5 (D50) and 0.13 ± 0.06 vs. 0.13 ± 0.07 (Homogeneity Index) for the PTV; 6.6 ± 4.0 vs. 8.4 ± 3.6 (V90) and 32.4 ± 3.8 vs. 46.6 ± 15.4 (V50) for the rectum; and 13.8 ± 1.8 vs. 13.3 ± 4.3 (V90) and 39.9 ± 2.0 vs. 38.4 ± 5.2 (V50) for the bladder. The R2 values in the big model were 0.251 and 0.755 for rectum and bladder, respectively, which were comparable to those from each institution model. The respective χ2 values in the big model were 1.009 and 1.002, which were closer to 1.0 than those from each institution model. The ratios of the outliers in the big model were also comparable to those from each institution model. The big model could generate a comparable VMAT plan quality compared with each single-institution model and therefore could possibly be shared with other institutions.

BACKGROUND/AIM: We aimed to clarify the TomoTherapy irradiation method for accurate dose delivery to the postoperative ear keloid with minimal exposure. MATERIALS AND METHODS: An electron beam of Elekta synergy and static and helical photon beams of TomoTherapy were delivered to the auricle and lobe of an anthropomorphic phantom compensated using a soft rubber bolus. The doses to the ear surface and the eyeballs and thyroid were measured using radiochromic film and glass dosimeters, respectively. RESULTS: Using static, helical, and electron beams, the respective doses to the ear surface were 97.9%, 103.0%, and 91.7% of the prescribed dose; the respective doses to the thyroid were 0.6, 0.8, and 2.4 cGy; the respective doses to the left eyeball were 3.3, 6.9, and 2.7 cGy. CONCLUSION: The static beam of the TomoTherapy can be safely used for treating ear keloids, while ensuring target dose. The helical photon beam spreads out the low-dose exposure.

PURPOSE: The purpose of this study was to evaluate the effect of a lead block for alveolar bone protection in image-guided high-dose-rate interstitial brachytherapy for tongue cancer. MATERIAL AND METHODS: We treated 6 patients and delivered 5,400 cGy in 9 fractions using a lead block. Effects of lead block (median thickness, 4 mm) on dose attenuation by distance were visually examined using TG-43 formalism-based dose distribution curves to determine whether or not the area with the highest dose is located in the alveolar bone, where there is a high-risk of infection. Dose re-calculations were performed using TG-186 formalism with advanced collapsed cone engine (ACE) for inhomogeneity correction set to cortical bone density for the whole mandible and alveolar bone, water density for clinical target volume (CTV), air density for outside body and lead density, and silastic density for lead block and its' silicon replica, respectively. RESULTS: The highest dose was detected outside the alveolar bone in five of the six cases. For dose-volume histogram analysis, median minimum doses delivered per fraction to the 0.1 cm3 of alveolar bone (D0.1cm3 TG-43, ACE-silicon, and ACE-lead) were 344.3 (range, 262.9-427.4) cGy, 336.6 (253.3-425.0) cGy, and 169.7 (114.9-233.3) cGy, respectively. D0.1cm3 ACE-lead was significantly lower than other parameters. No significant difference was observed between CTV-related parameters. CONCLUSIONS: The results suggested that using a lead block for alveolar bone protection with a thickness of about 4 mm, can shift the highest dose area to non-alveolar regions. In addition, it reduced D0.1cm3 of alveolar bone to about half, without affecting tumor dose.

PURPOSE: The efficiency of protective equipment for the brain has not been verified at the left anterior oblique (LAO) position, which is commonly used in clinical procedures. The purpose of this study was to investigate radiation exposure of the brain in interventional radiology (IR) and the shielding ability of a new protective flap. METHODS: We made a flap that combined a protective cap with a left lateral face shield. The flap was made of tungsten-containing rubber (TCR). An anthropomorphic head phantom was placed at the physician's position, and air kerma rates (μGy/min and μGy/15s) were measured by electronic dosimeter at three locations: the surface of the left side of the head, and the left and right temporal lobes with the protective cap and the flap in fluoroscopy and cine modes. The X-ray tube was at the lower left side of the physician, and its angles were LAO60 and LAO60CAU40. The tube voltage (95-125 kV), tube current (4.7-732 mA), and air kerma rate (27.8-1078 mGy/min) were automatically adjusted by the X-ray system. We obtained the cap and the flap shielding efficiencies. RESULTS: In cine mode at LAO60CAU40, the shielding efficiencies on the surface of the left side of the head and left temporal lobe with the cap were 92.6% and 5.1%, respectively, and the corresponding shielding efficiencies with the flap were 92.5% and 86.1%, respectively. The flap can reduce radiation exposure of the brain more than the cap alone. CONCLUSIONS: At the left anterior oblique in interventional radiology, the flap can reduce exposure to the brain.

In this study, we aim to clarify the dosimetric characteristics of a real time variable shape rubber containing tungsten (STR) as a thin bolus in 6-MV photon radiotherapy. The percentage depth doses (PDDs) and lateral dose profiles (irradiation field = 10 × 10  cm2) in the water-equivalent phantom were measured and compared between no bolus, a commercial 5-mm gel bolus, and 0.5-, 1-, 2-, and 3-mm STR boluses. The characteristics of the PDDs were evaluated according to relative doses at 1 mm depth (D1mm) and depth of maximum dose (dmax). To determine the distance of the shift caused by the STR bolus, the PDD value at a depth of 100 mm without a bolus was obtained. For each STR thickness, the difference between the depth corresponding to this PDD value and 100 mm was calculated. The penumbra size and width of the 50% dose were evaluated using lateral dose profiles. The D1mm with no bolus, 5-mm gel bolus, and 0.5-, 1-, 2-, and 3-mm STR boluses were 47.6%, 91.5%, 78.2%, 86.6%, 89.3%, and 89.4%, respectively, and the respective dmax values were 15, 10, 13, 12, 11, and 10 mm. The shifting distance of the 0.5-, 1-, 2-, and 3-mm STR boluses were 2.7, 4.4, 4.8, and 4.9 mm, respectively. There were no differences for those in lateral dose profiles. The 1-mm-thick STR thin bolus shifted the depth dose profile by 4.4 mm and could be used as a customized bolus for photon radiotherapy.

We have developed soft rubber (SR) bolus that can be shaped in real-time by heating flexibly and repeatedly. This study investigated whether the SR bolus could be used as an ideal bolus, such as not changing of the beam characteristics and homogeneity through the bolus and high plasticity to adhere a patient in addition to real-time shapeable and reusability, in electron radiotherapy. Percentage depth doses (PDDs) and lateral dose profiles (LDPs) were obtained for 4, 6, and 9 MeV electron beams and were compared between the SR and conventional gel boluses. For the LDP at depth of 90% dose, the penumbra as lateral distance between the 80% and 20% isodose lines (P80-20) and the width of 90% dose level (r90) were compared. To evaluate adhesion, the air gap volume between the boluses and nose of a head phantom was evaluated on CT image. The dose profiles along the center axis for the 6 MeV electron beam with SR, gel, and virtual boluses (thickness = 5 mm) on the head phantom were also calculated for the irradiation of 200 monitor unit with a treatment planning system and the depth of the maximum dose (dmax) and maximum dose (Dmax) were compared. The PDDs,P80-20, andr90between the SR and gel boluses corresponded well (within 2%, 0.4 mm, and 0.7 mm, respectively). The air gap volumes of the SR and gel boluses were 3.14 and 50.35 cm3, respectively. Thedmaxwith SR, gel and virtual boluses were 8.0, 6.0, and 7.0 mm (no bolus: 12.0 mm), and theDmaxvalues were 186.4, 170.6, and 186.8 cGy, respectively. The SR bolus had the equivalent electron beam characteristics and homogeneity to the gel bolus and achieved excellent adhesion to a body surface, which can be used in electron radiotherapy as an ideal bolus.

Positron emission tomography (PET)/CT is an essential imaging modality for the management of various diseases. Increasing numbers of PET/CT examinations are carried out across the world and deliver benefits to patients; however, there are concerns about the cumulative radiation doses from these examinations in patients. Compared to the radiation exposure delivered by CT, there have been few reports on the frequency of patients with a cumulative effective radiation dose of ≥100 mSv from repeated PET/CT examinations. The emerging dose tracking system facilitates surveys on patient cumulative doses by PET/CT because it can easily wrap up exposure doses of PET radiopharmaceuticals and CT. Regardless of the use of a dose tracking system, implementation of justification for PET/CT examinations and utilisation of dose reduction measures are key issues in coping with the cumulative dose in patients. Despite all the advantages of PET/MRI such as eliminating radiation exposure from CT and providing good tissue contrast in MRI, it is expensive and cannot be introduced at every facility; thus, it is still necessary to utilise PET/CT with radiation reduction measures in most clinical situations.

PURPOSE: We investigated the performance of the simplified knowledge-based plans (KBPs) in stereotactic body radiotherapy (SBRT) with volumetric-modulated arc therapy (VMAT) for lung cancer. MATERIALS AND METHODS: For 50 cases who underwent SBRT, only three structures were registered into knowledge-based model: total lung, spinal cord, and planning target volume. We performed single auto-optimization on VMAT plans in two steps: 19 cases used for the model training (closed-loop validation) and 16 new cases outside of training set (open-loop validation) for TrueBeam (TB) and Halcyon (Hal) linacs. The dosimetric parameters were compared between clinical plans (CLPs) and KBPs: CLPclosed, KBPclosed-TB and KBPclosed-Hal in closed-loop validation, CLPopen, KBPopen-TB and KBPopen-Hal in open-loop validation. RESULTS: All organs at risk were comparable between CLPs and KBPs except for contralateral lung: V5 of KBPs was approximately 3%-7% higher than that of CLPs. V20 of total lung for KBPs showed comparable to CLPs; CLPclosed vs. KBPclosed-TB and CLPclosed vs. KBPclosed-Hal: 4.36% ± 2.87% vs. 3.54% ± 1.95% and 4.36 ± 2.87% vs. 3.54% ± 1.94% (P = 0.54 and 0.54); CLPopen vs. KBPopen-TB and CLPopen vs. KBPopen-Hal: 4.18% ± 1.57% vs. 3.55% ± 1.27% and 4.18% ± 1.57% vs. 3.67% ± 1.26% (P = 0.19 and 0.27). CI95 of KBPs with both linacs was superior to that of the CLP in closed-loop validation: CLPclosed vs. KBPclosed-TB vs. KBPclosed-Hal: 1.32% ± 0.12% vs. 1.18% ± 0.09% vs. 1.17% ± 0.06% (P < 0.01); and open-loop validation: CLPopen vs. KBPopen-TB vs. KBPopen-Hal: 1.22% ± 0.09% vs. 1.14% ± 0.04% vs. 1.16% ± 0.05% (P ≤ 0.01). CONCLUSIONS: The simplified KBPs with limited number of structures and without planner intervention were clinically acceptable in the dosimetric parameters for lung VMAT-SBRT planning.

PURPOSE: Skin collimation provides a sharp penumbra for electron beams, while the effect of bremsstrahlung from shielding materials is a concern. This phantom study was conducted to evaluate the safety and efficacy of a real-time variable shape rubber containing-tungsten (STR) that can be placed on a patient's skin. METHODS: Electron beam profiles were acquired with the STR placed on a water-equivalent phantom and low melting-point alloy (LMA) placed at the applicator according to commonly used procedures (field sizes: 20- and 40-mm diameters). Depth and lateral dose profiles for 6- and 12-MeV electron beams were obtained by Monte Carlo (MC) simulations and were benchmarked against film measurements. The width of the off-axis distance between 80% and 20% doses (P80-20 ) and the maximum dose were obtained from the lateral dose profiles. Bremsstrahlung emission was analyzed by MC simulations at the depth of maximum dose (R100 ). RESULTS: The depth dose profiles calculated by the MC simulations were consistently within 2% of the measurements. The P80-20 at R100 for 20- and 40-mm diameters were 4.0 mm vs. 7.6 mm (STR vs. LMA) and 4.5 mm vs. 9.2 mm, respectively, for the 6-MeV electron beam with 7.0-mm-thick STR, and 2.7 mm vs. 5.6 mm and 4.5 mm vs. 7.1 mm, respectively, for the 12-MeV electron beam with 12.0-mm-thick STR. A hotspot was not observed on the lateral dose profiles obtained with the STR at R100 . The bremsstrahlung emission under the region shielded by the STR was comparable to that obtained with the LMA, even though the STR was placed on the surface of the phantom. CONCLUSIONS: Skin collimator with STR provided superior dosimetric characteristics and comparable bremsstrahlung emission to LMA collimator at the applicator. STR could be a new tool for the safe and efficient delivery of electron radiotherapy.

BACKGROUND/AIM: We investigated the dosimetric characteristics of electron radiotherapy for auricular keloid using real-time variable-shape tungsten rubber (STR). PATIENTS AND METHODS: For the first evaluation, STR was shaped into a rectangular irradiation field (3.0×5.0 cm2). In the next step, the STR was reshaped to fit the target (3.5×6.5 cm2) for the second evaluation. Percentage depth doses (PDDs) and lateral dose profiles were obtained with 6-MeV electron beams and compared with those of low-melting-point lead (LML). RESULTS: Compared to the LML on electron applicator, PDD differences were within 0.4 mm, while the penumbras as width of 20-80% dose levels were smaller (maximum reductions: 75.8% and 82.9% at first and second evaluations, respectively). The treatment process of shaping the STR, decision on output, and irradiation was completed within 45 min. CONCLUSION: Electron radiotherapy using STR for keloid can be performed with excellent dose distribution in a short time. First clinical experience found the STR is suitable for use in individualized and immediate electron radiotherapy.

Background: The aim of this study was to investigate the performance of the RapidPlan (RP ) using models registered pseudostructures, and to determine how many structures are required for automatic optimization of volumetric modulated arc therapy (VMAT) for postoperative uterine cervical cancer. Materials and methods: Pseudo-structures around the PTV were retrospectively contoured for patients who had completed treatment at five institutions. For 22 common patients, plans were generated with a single optimization for models with two (RP_2), four (RP_4), and five (RP_5) registered structures, and the dosimetric parameters of these models were compared with a clinical plan with several optimizations. Results: Most dosimetric parameters showed no major differences between each RP model. In particular, the rectum Dmax, V50Gy, and V40Gy with RP_2, RP_4, and RP_5 were not significantly different, and were lower than those of the clinical plan. The average proportions of plans achieving acceptable criteria for dosimetric parameters were close to 100% for all models. Using RP_2, the average time for the VMAT planning was reduced by 88 minutes compared with the clinical plan. Conclusion: The RapidPlan model with two registered pseudo-structures could generate clinically acceptable plans while saving time.

PURPOSE: Knowledge-based planning (KBP) has disadvantages of high monitor unit (MU) and complex multi-leaf collimator (MLC) motion. We investigated the optimal aperture shape controller (ASC) level for the KBP to reduce these factors in volumetric modulated arc therapy (VMAT) for prostate cancer. METHODS: The KBP model was created based on 51 clinical plans (CPs) of patients who underwent the VMAT for prostate cancer. Another 10 CPs were selected randomly, and the KBPs with/without ASC, changed stepwise from very low (KBP-VL) to very high (KBP-VH), were performed with a single auto-optimization. The parameters of dose-volume histograms (DVHs) and MLC performance metrics were evaluated. We obtained the modulation complexity score for VMAT (MCSv), closed leaf score (CLS), small aperture score (SAS), leaf travel (LT), and total MU. RESULTS: The ASC did not affect the DVH parameters negatively. The following comparisons of MLC performance were obtained (KBP vs. KBP-VL vs. KBP-VH, respectively): 0.25 vs. 0.27 vs. 0.30 (MCSv), 0.19 vs. 0.18 vs. 0.16 (CLS), 0.50 vs. 0.45 vs. 0.40 (SAS10 mm), 0.73 vs. 0.68 vs. 0.63 (SAS20 mm), 768.35 mm vs. 671.50 mm vs. 551.32 mm (LT), and 672.87 vs. 642.36 vs. 607.59 (MU). There were significant differences between KBP and KBP-VH for MCSv and LT (p<0.05). CONCLUSIONS: The KBP using an ASC set to the very high level could reduce the complexity of MLC motion significantly more without deterioration of the DVH parameters compared with the KBP in VMAT for prostate cancer.

PURPOSE: This study investigated whether real-time variable shape tungsten rubber (STR) could be applied for nail radiation protection in total skin electron beam (TSEB) therapy. METHODS: Simulated finger phantoms were made from syringes filled with physiological saline of volumes 5, 10, 20, and 30 ml (inner diameters of 14.1, 17.0, 21.7, and 25.3 mm, respectively). Gafchromic film was applied to the phantom, and lead (thickness 1-3 mm) or STR (thickness 1-4 mm) with an area of 4´1.5 cm was used to cover the film. A 6 MeV electron beam with an 8 mm acrylic board was then used to irradiate the phantom. The source-surface distance (SSD) was 444 cm, the field size was 36´36 cm at SSD of 100 cm without an electron applicator, and the monitor unit was 2000 MU. The shielding rates were obtained from the dose profiles. RESULTS: The mean values of the shielding rate values for all phantoms were 50.1, 97.6, and 98.7% for 1, 2, and 3 mm of lead, respectively, and -13.6, 53.9, 91.2, and 99.4% for 1, 2, 3, and 4 mm of STR, respectively. CONCLUSION: STR with a thickness of 4 mm had the same shielding properties as lead with a thickness of 3 mm, which was an approximately 100% shielding rate. STR could therefore be used in TSEB therapy instead of lead.

BACKGROUND: An O-ring gantry-type linear accelerator (LINAC) with a 6-MV flattening filter-free (FFF) photon beam, Halcyon, includes a reference beam that contains representative information such as the percent depth dose, profile and output factor for commissioning and quality assurance. However, because it does not provide information about the field size, we proposed a method to determine all field sizes according to all depths for radiation therapy using simplified sigmoidal curve fitting (SCF). METHODS: After mathematical definition of the SCF using four coefficients, the defined curves were fitted to both the reference data (RD) and the measured data (MD). For good agreement between the fitting curve and the profiles in each data set, the field sizes were determined by identifying the maximum point along the third derivative of the fitting curve. The curve fitting included the field sizes for beam profiles of 2 × 2, 4 × 4, 6 × 6, 8 × 8, 10 × 10, 20 × 20 and 28 × 28 cm2 as a function of depth (at 1.3, 5, 10 and 20 cm). The field size results from the RD were compared with the results from the MD using the same condition. RESULTS: All fitting curves show goodness of fit, R2, values that are greater than 0.99. The differences in field size between the RD and the MD were within the range of 0 to 0.2 cm. The smallest difference in the field sizes at a depth of 10 cm, which is a surface-to-axis distance, was reported. CONCLUSION: Application of the SCF method has been proven to accurately capture the field size of the preconfigured RD and the measured FFF photon beam data for the Halcyon system. The current work can be useful for beam commissioning as a countercheck methodology to determine the field size from RD in the treatment planning system of a newly installed Halcyon system and for routine quality assurance to ascertain the correctness of field sizes for clinical use of the Halcyon system.

Dosimetric evaluation and variation assessment were performed with two knowledge-based planning (KBP) models created at different periods for volumetric-modulated arc therapy (VMAT) for prostate cancer at five institutes. The first and second models (F- and S-models) for KBP were created before April 2017 and April 2019, respectively. The S-model was created using feedback plans from the F-model. Dose evaluation was compared between the two models using the same two computed tomography (CT) datasets and structures. The evaluation metrics were the dose received by 95.0% and 2.0% of the planning target volume (PTV); dose-volume parameters to the rectum and bladder as V90, V80, and V50; and monitor unit (MU). Dosimetric variation was compared by exporting estimated dose-volume histograms for each model to the Model Analytics website and assessing the organ at risk volume. There were no dosimetric differences between the two models for PTV. The V50 of the rectum in the S-model had improved compared to that of the F-model (case I: 49.3 ± 15.6 and 43.5 ± 15.2 [p = 0.08]; case II: 42.5 ± 16.9 and 36.0 ± 15.6 [p = 0.138]). The differences in other parameters were within ± 1.8% between the rectum and the bladder. The MU was slightly higher in the S-model than in the F-model, and dosimetric variation was reduced to the rectum and bladder among all the institutes. The polished S-model for KBP could be used for standardization of the plan quality and sharing of KBP models in VMAT for prostate cancer.

This study aimed to evaluate the possibility of reducing the imaging dose for image-guided radiotherapy by using planar kilovoltage orthogonal imaging and fiducial markers (kV-FM). We tested kilovoltage planar images under clinical imaging conditions for the pelvis (75 kVp, 200 mA, 50 ms) at a decreasing tube current (from 200 to 10 mA). Imaging doses were measured with a semiconductor detector. The visibility of the kV-FM, aspects of image quality (spatial resolution, low contrast resolution), and the resultant image registration reproducibility were evaluated using various shapes (folded, linear, tadpole-like) of fiducial markers containing 0.5% iron [Gold Anchor™ (GA); Naslund Medical AB, Huddinge, Sweden]. The GA phantom was created by placing these variously shaped GAs in an agar phantom. The imaging doses with 200 and 10 mA were approximately 0.74 and 0.04 mGy and they were correlated to the tube current (R2  = 0.999). Regardless of the marker's shape, the GA phantom ensured visibility even when the tube current was reduced to the minimum value (10 mA). The low contrast resolution was gradually decreased at less than 50 mA, but the spatial resolution did not change. Although the auto-registration function could not be used, manual-registration could be achieved with an accuracy of within 1 mm, even when the imaging dose was reduced to 1/20 of the clinical imaging condition for the pelvis. When using the GA as the fiducial marker, the imaging dose could be reduced to 1/20 of that used clinically while maintaining the accuracy of manual-registration using the kV-FM for image-guided radiotherapy of the pelvis.

PURPOSE: This study performed the accurate measurements of beam profiles with a new rigid board, which was consistent with the supplied reference beam profiles (RBPs) for clinical Halcyon model. METHODS: Percentage depth doses (PDDs), lateral and diagonal dose profiles were measured and compared with RBPs. A water tank was set on the rigid board bridged Halcyon bore without sagging and source-to-surface distance was 90.0 cm. Field sizes were from 2.0 to 28.0 cm squares and depths of lateral and diagonal dose profiles were 1.3, 5.0, 10.0, and 20.0 cm. For the PDD, the depth of maximum dose (dmax), PDD value at depth of 10.0 cm (PDD10), and absolute dose difference (DD) between RBP and measured beam profiles (MBP) were evaluated. For lateral and diagonal dose profiles, DDs for the whole and divided areas (central, shoulder, and extended areas) defined by third derivative, and distance-to-agreement (DTA) in the penumbra area were evaluated. RESULTS: For PDDs, the differences of dmax and PDD10 and DD beyond the dmax were within 1.0 mm, 0.3%, and 1.0%, respectively. For lateral and diagonal dose profiles, the DDs reached approximately 5.0% in the whole area because of penumbra area, while the DDs in the central, shoulder, and extended areas were within 1.0%, 2.0%, and 1.0%, respectively. The DTAs in the penumbra area were within 0.8 mm. CONCLUSIONS: The supplied RBPs can be used clinically owing to the good agreement with the accurate MBPs with rigid board.

Containing 80% tungsten by weight, tungsten functional paper (TFP) is a radiation-shielding material that is lightweight, flexible, disposable, and easy to cut. Through experimental measurements and Monte Carlo simulations, we investigated the feasibility of using TFP as a bolus in electron beam radiotherapy. Commercial boluses of thickness 5 and 10 mm and from one to nine layers of TFPs (0.3-2.7 mm) were positioned on the surface of water-equivalent phantoms. The percentage depth dose curves and transverse dose profiles were measured using a 9-MeV electron beam from a clinical linear accelerator. Normalized to the value at the depth of maximum dose without bolus, the relative doses at the phantom surface for no bolus, 5-mm bolus, 10-mm bolus, 1 TFP, 3 TFPs, 6 TFPs, and 9 TFPs were 78%, 88%, 92%, 84%, 92%, 102%, and 112%, respectively; the therapeutic depths corresponding to a 90% dose level were 29.1 mm, 22.7 mm, 17.7 mm, 26.6 mm, 23.2 mm, 19.3 mm, and 15.8 mm, respectively. The TFP contributed to increased skin dose and provided dose uniformity within the target volume. However, it also resulted in increased lateral constriction and penumbra width. The results of Monte Carlo simulation produced similar trends as the experimental measurements. Our findings suggest that using TFP as a novel thin and flexible skin bolus for electron beam radiotherapy is feasible.

This study characterized the plan complexity of the dual-layer multi-leaf collimator (MLC) performance for volumetric modulated arc therapy (VMAT) in Halcyon. Plan complexity metrics were computed independently for each MLC layer (proximal and distal): modulation complexity score (MCS), plan averaged beam area, irregularity, and modulation (PA, PI, and PM) were obtained. These were investigated when weighted by proportions of the effective proximal MLC and distal MLC (MCSw, PAw, PIw, and PMw). Conventional plan complexity metrics for the effective 5.0 mm resolution MLC (MCS5, PA5, PI5, PM5), small aperture score (SAS), effective distal MLC score (EDS), and MU were also evaluated. Forty-five consecutive VMAT plans were analyzed retrospectively for treatment sites of the prostate, head and neck (HN), and other parts. The mean values of the metrics for proximal MLC and distal MLC were 0.310 and 0.245 (MCS), 71.09 cm2 and 55.92 cm2 (PA), 6.24 and 10.19 (PI), and 0.593 and 0.645 (PM), respectively. The degree of plan complexity in the distal MLC was larger than in the proximal MLC. The percentage of the effective distal MLC was higher than that of the proximal MLC (mean EDS = 0.555). The MCSw, PAw, PIw, and PMw showed significant differences between the prostate and HN groups like the PA5, PI5, and PM5; however, the MCS5 did not. Additionally, the MCS5 correlated with MU and PM5, while the MCSw correlated with SAS and PA5. The plan complexity for each MLC layer and subsequently combining these complexities might be useful to better understand the dual-layer MLC performance.

The present study aimed to evaluate whether knowledge-based plans (KBP) from a single optimization could be used clinically, and to compare dose-volume histogram (DVH) parameters and plan quality between KBP with (KBPCONST) and without (KBPORIG) manual objective constraints and clinical manual optimized (CMO) plans for pharyngeal cancer. KBPs were produced from a system trained on clinical plans from 55 patients with pharyngeal cancer who had undergone intensity-modulated radiation therapy or volumetric-modulated arc therapy (VMAT). For another 15 patients, DVH parameters of KBPCONST and KBPORIG from a single optimization were compared with CMO plans with respect to the planning target volume (D98%, D50%, D2%), brainstem maximum dose (Dmax), spinal cord Dmax, parotid gland median and mean dose (Dmed and Dmean), monitor units and modulation complexity score for VMAT. The Dmax of spinal cord and brainstem and the Dmed and Dmean of ipsilateral parotid glands were unacceptably high for KBPORIG, although the KBPCONST DVH parameters met our goal for most patients. KBPCONST and CMO plans produced comparable DVH parameters. The monitor units of KBPCONST were significantly lower than those of the CMO plans (P < 0.001). Dose distribution of the KBPCONST was better than or comparable to that of the CMO plans for 13 (87%) of the 15 patients. In conclusion, KBPORIG was found to be clinically unacceptable, while KBPCONST from a single optimization was comparable or superior to CMO plans for most patients with head and neck cancer.

BACKGROUND/AIM: We aimed to elucidate the pathological findings following acute and late re-irradiation in a preclinical model. MATERIALS AND METHODS: Mice were divided into five treatment groups: sham-irradiation (Sham-IR), 10-12 Gy (Single IR Acute), 15 Gy (Single IR Late), 15 Gy followed by 10-12 Gy re-irradiation 7 days later (Re-IR Acute), or 15 Gy followed by 10-12 Gy re-irradiation 12 weeks later (Re-IR Late). Mice were sacrificed after either single irradiation or re-irradiation for pathological assessment. RESULTS: The Re-IR Late group had significantly lower numbers of crypts with apoptotic cells than those observed in mice in the Single IR Acute group. There were no significant differences between the Single IR Acute and re-IR Acute groups in cell proliferation or in a crypt survival assay. CONCLUSION: Re-irradiation with a long interval after the first irradiation may cause similar acute biological effects in normal intestine as observed following irradiation without re-irradiation.

PURPOSE: We investigated whether a tungsten functional paper (TFP) shield and/or organ-based tube current modulation (TCM) can reduce the dose to the eye lens. MATERIALS AND METHODS: All scans were performed using our routine head examination protocol (spiral acquisition, 120 kVp, noise Index 3.5) with an anthropomorphic head phantom. The dose reduction rate was measured by the following methods with a scintillation fiber optic dosimeter: (a) without any dose reduction techniques (Original scan), (b) TFP shield, (c) TCM, and (d) TFP shield plus TCM. Image noise and CT number were obtained and compared between the three groups. In addition, image noise in method (d) was measured with varying distances between the TFP shield and eye lens. RESULTS: The reduction rates using TFP shield, TCM, and TFP shield plus TCM compared with those for the Original scan were 17.8 %, 13.6 %, and 27.7 %, respectively. Image noise (mean ± standard deviation) in the anterior region for the Original scan, TFP shield, TCM, and TFP shield plus TCM were 4.1 ± 0.2, 4.6 ± 0.2, 4.4 ± 0.3, and 5.0 ± 0.2, while the CT numbers were 19.3 ± 0.8, 23.8 ± 0.8, 19.6 ± 0.8, and 24.1 ± 0.8, respectively. Increasing the distance between the TFP and the eye significantly decreased the CT number when using TFP shield plus TCM (p < .05). CONCLUSION: TFP shield plus TCM reduced the dose to the eye lens in head CT while maintaining image quality with an air gap between the TFP and skin surface.

PURPOSE: This study aimed to investigate the influence of cleaned-up knowledge-based treatment planning (KBP) models on the plan quality for volumetric-modulated arc therapy (VMAT) of prostate cancer. MATERIALS AND METHODS: Thirty prostate cancer VMAT plans were enrolled and evaluated according to four KBP modeling methods as follows: (1) model not cleaned - trained by fifty other clinical plans (KBPORIG); (2) cases cleaned by removing plans that did not meet all clinical goals of the dosimetric parameters, derived from dose-volume histogram (DVH) (KBPC-DVH); (3) cases cleaned outside the range of ±1 standard deviation through the principal component analysis regression plots (KBPC-REG); and (4) cases cleaned using both methods (2) and (3) (KBPC-ALL). Rectal and bladder structures in the training models numbered 34 and 48 for KBPC-DVH, 37 and 33 for KBPC-REG, and 26 and 33 for KBPC-ALL, respectively. The dosimetric parameters for each model with one-time auto-optimization were compared. RESULTS: All KBP models improved target dose coverage and conformity and provided comparable sparing of organs at risks (rectal and bladder walls). There were no significant differences in plan quality among the KBP models. Nevertheless, only the KBPC-ALL model generated no cases of >1% V78 Gy (prescribed dose) to the rectal wall, whereas the KBPORIG, KBPC-DVH, and KBPC-REG models included two, four, and three cases, respectively, which were difficult to overcome with KBP because the planning target volume (PTV) and rectum regions overlapped. CONCLUSIONS: The cleaned-up KBP model based on DVH and regression plots improved plan quality in the PTV-rectum overlap region.

PURPOSE: This study investigated the dosimetric characteristics of electron beams shaped with a real-time shapeable tungsten-containing rubber (STR) collimator. METHODS: Circular irradiation fields of 40 mm diameter were shaped using STR or low melting-point alloy (LMA) placed on the electron applicator. The STR heated with approximately 70-degree warm water was molded into the template bottom of the applicator. Percent depth doses (PDDs) and lateral dose profiles of 6 and 12 MeV electron beams were measured and compared between STR and LMA. For the PDDs, the depths of maximum dose (dmax), 90% dose (d90), and 80% dose (d80) were evaluated. For the lateral dose profiles, penumbra as the width of the off-axis distance from 80% to 20% doses and treatment diameter covering over 90% dose were evaluated at the surface, dmax, d90, and d80. The transmission of the STR was also investigated at thicknesses fit to electron applicator for 6 and 12 MeV electron beams. RESULTS: The STR was softened with 70-degree warm water. Therefore, it was easy to mold it and attach the applicator. The PDDs and penumbras at the surface, dmax, d90, and d80 for the STR were almost equal to those for the LMA with 6 and 12 MeV electron beams. The treatment diameters covering over 90% dose for the irradiation fields with 40 mm diameter at dmax (LMA vs. STR) were 20.9 vs. 21.1 mm and 19.2 vs. 18.4 mm for 6 and 12 MeV electron beams, respectively. The transmission of the STR was almost same as that of LMA. CONCLUSIONS: The dosimetric characteristics of the STR on the electron applicator were almost same as those of the LMA. The heated STR was shaped easily, flexibly, and immediately. The STR can be used as a substitute for LMA in electron radiotherapy.

PURPOSE: Novel linac improvements in speed of gantry, collimator, leaf and dose rate may increase the time-efficiency of volumetric modulated arc therapy (VMAT) delivery, however remains to be investigated. In this study, a fast-rotating O-ring linac (Halcyon) with fast moving leaves is compared with a general linac (TrueBeam: TB) in terms of plan quality for VMAT of C-shape, prostate, multi target and, head and neck (H&N) cases from AAPM TG-119. MATERIALS AND METHODS: For the four test cases, VMAT planning was performed using single to four-arc VMAT on a Halcyon and using single to three-arc VMAT on a TrueBeam. Same conditions for optimization were used in each test case. Target coverage metrics and organ at risks (OAR) dose were compared. Monitor unit (MU) and irradiation time in each plan were also compared. RESULTS: In all cases, single-arc plans of Halcyon were inferior to TB plans on dose objectives. Conformity index (CI) to outer target of C-shape case was better for Halcyon (1-arc: 1.242, 2-arc: 1.202, 3-arc: 1.198, 4-arc: 1.181) than for TB (1-arc: 1.247, 2-arc: 1.211, 3-arc: 1.211) except to single arc. D5 (Gy) of core for C-shape case was better for halcyon (1-arc: 23.29, 2-arc: 21.01, 3-arc: 20.64, 4-arc: 20.47) than for TB (1-arc: 24.04, 2-arc: 22.94, 3-arc: 23.04). Calculated MU was smaller for Halcyon than for TB. In addition, Halcyon is more faster than TB because mechanical movements were improved. CONCLUSION: For VMAT plan in each case, Halcyon as well or better at the plan quality of two or three arcs on TB while reducing the delivery time.

This study investigates whether a novel tungsten-containing rubber shield could be used as substitute shielding material in interventional radiology to reduce the occupational exposure of operators to scattered radiation from a patient. The tungsten-containing rubber is a lead-free radiation-shielding material that contains as much as 90% tungsten powder by weight. Air kerma rates of scattered radiation from solid-plate phantoms, simulating a patient, were measured with a semiconductor dosimeter at the height of the operator's eye (1,600 mm from the floor), chest (1,300 mm), waist (1,000 mm), and knee (600 mm) with and without tungsten-containing rubber shielding (1-5 mm thickness). The tungsten-containing rubber and a commercial shielding material (RADPAD) were affixed onto the phantom on the operator's side, and reductions in air kerma rates were compared. Reduction rates for tungsten-containing rubber shielding with thicknesses of 1, 2, 3, 4, and 5 mm at each height level were as follows: 70.37 ± 0.40%, 72.17 ± 0.29%, 72.95 ± 0.31%, 72.58 ± 0.35%, and 73.63 ± 0.63% at eye level; 76.36 ± 0.19%, 77.13 ± 0.10%, 77.36 ± 0.14%, 77.62 ± 0.25%, and 77.66 ± 0.14% at chest level; 67.78 ± 0.31%, 68.12 ± 0.19%, 68.88 ± 0.28%, 68.97 ± 0.14%, and 68.85 ± 0.45% at waist level; and 0.14 ± 0.94%, 0.72 ± 0.56%, 1.08 ± 0.74%, 1.77 ± 0.80%, and 1.79 ± 1.82% at knee level, respectively. Reduction rates with RADPAD were 61.80 ± 0.67%, 60.33 ± 0.61%, 64.70 ± 0.25%, and 0.14 ± 0.66% at eye, chest, waist, and knee levels, respectively. The shielding ability of the 1 mm tungsten-containing rubber was superior to that of RADPAD. The tungsten-containing rubber could be employed to minimize an operator's radiation exposure instead of the commercial shielding material in interventional radiology.

AIM: To evaluate the success of a patient-specific intensity modulated radiation therapy (IMRT) quality assurance (QA) practice for prostate cancer patients across multiple institutions using a questionnaire survey. BACKGROUND: The IMRT QA practice involves different methods of dose distribution verification and analysis at different institutions. MATERIALS AND METHODS: Two full-arc volumetric modulated arc therapy (VMAT) plan and 7 fixed-gantry IMRT plan with DMLC were used for patient specific QA across 22 institutions. The same computed tomography image and structure set were used for all plans. Each institution recalculated the dose distribution with fixed monitor units and without any modification. Single-point dose measurement with a cylindrical ionization chamber and dose distribution verification with a multi-detector or radiochromic film were performed, according to the QA process at each institution. RESULTS: Twenty-two institutions performed the patient-specific IMRT QA verifications. With a single-point dose measurement at the isocenter, the average difference between the calculated and measured doses was 0.5 ± 1.9%. For the comparison of dose distributions, 18 institutions used a two or three-dimensional array detector, while the others used Gafchromic film. In the γ test with dose difference/distance-to-agreement criteria of 3%-3 mm and 2%-2 mm with a 30% dose threshold, the median gamma pass rates were 99.3% (range: 41.7%-100.0%) and 96.4% (range: 29.4%-100.0%), respectively. CONCLUSION: This survey was an informative trial to understand the verification status of patient-specific IMRT QA measurements for prostate cancer. In most institutions, the point dose measurement and dose distribution differences met the desired criteria.

PURPOSE: This study aimed to clarify the inter-planner variation of plan quality in knowledge-based plans created by nine planners. METHODS: Five hypofractionated prostate-only (HPO) volumetric modulated arc therapy (VMAT) plans and five whole-pelvis (WP) VMAT plans were created by each planner using a knowledge-based planning (KBP) system. Nine planners were divided into three groups of three planners each: Senior, Junior, and Beginner. Single optimization with only priority modification for all objectives was performed to stay within the dose constraints. The coefficients of variation (CVs) for dosimetric parameters were evaluated, and a plan quality metric (PQM) was used to evaluate comprehensive plan quality. RESULTS: Lower CVs (<0.05) were observed at dosimetric parameters in the planning target volume for both HPO and WP plans, while the CVs in the rectum and bladder for WP plans (<0.91) were greater than those for HPO plans (<0.17). The PQM values of HPO plans for Cases1-5 (average ± standard deviation) were 41.2 ± 7.1, 40.9 ± 5.6, and 39.9 ± 4.6 in the Senior, Junior, and Beginner groups, respectively. For the WP plans, the PQM values were 51.9 ± 6.3, 47.5 ± 4.3, and 40.0 ± 6.6, respectively. The number of clinically acceptable HPO and WP plans were 13/15 and 11/15 in the Senior group, 13/15 and 10/15 plans in the Junior group, and 8/15 and 2/15 plans in the Beginner group, respectively. CONCLUSION: Inter-planner variation in the plan quality with RapidPlan remains, especially for the complicated VMAT plans, due to planners' heuristics.

PURPOSE: The influence of the offset distance from treatment target to gantry isocenter (GIC) on the dosimetric parameter and irradiation time was investigated using TomoTherapy METHODS: The reference position was defined as the centers of both the I'mRT phantom and planning target volume (PTV) with a spherical of 4 cm diameter aligned with the GIC. The dose calculations were performed in two offset methods with 2 and 12 Gy/fr, Method 1. The PTV was moved from 0.0 to 12.5 cm along the RL direction and -5.0 to 5.0 cm along the AP direction (PTV offset), Method 2. The phantom was moved from 0.0 to -7.5 cm along the RL direction and -5.0 to 5.0 cm along the AP direction (Phantom offset). The maximum, minimum and mean doses, homogeneity index, conformity index, irradiation time, and monitor unit were compared. RESULTS: The irradiation times increased with increasing PTV offset. The increases in the irradiation time were 54.4% and 40.8% at PTV offsets of 12.5 cm along the RL direction for 2 and 12 Gy/fr, while the increases were 20.1% and 15.0% at a PTV offset of 5.0 cm along the AP direction. An increased irradiation time was not observed for the phantom offset. The offset didn't affect the other parameters. CONCLUSIONS: The PTV location offset of ≥5 cm from the GIC along the RL and AP axes increased the irradiation time; therefore, the PTV should be aligned with the GIC as much as possible to reduce the irradiation time on TomoTherapy.

BACKGROUND: This study clarified the mechanical performance of volumetric modulated arc therapy (VMAT) plans for prostate cancer generated with a commercial knowledge-based treatment planning (KBP) and whether KBP system could be applied clinically without any major problems with mechanical performance. METHODS: Thirty consecutive prostate cancer patients who underwent VMAT using extant clinical plans were evaluated. The mechanical performance and dosimetric accuracy of the single optimized KBPs, which were trained with other 51 clinical plans, were compared with the clinical plans. The mechanical performance metrics were mean field area (MFA), mean asymmetry distance (MAD), cross-axis score (CAS), closed leaf score (CLS), small aperture score (SAS), leaf travel (LT), modulation complexity score (MCSv), and monitor unit (MU). The γ passing rates were evaluated with ArcCheck and EBT3 film. RESULTS: The mean mechanical performance metrics (clinical plan vs. KBP) were as follows: 18.28 cm2 vs. 17.25 cm2 (MFA), 21.08 mm vs. 20.47 mm (MAD), 0.54 vs. 0.55 (CAS), 0.040 vs. 0.051 (CLS), 0.20 vs. 0.23 (SAS5mm), 458.5 mm vs. 418.8 mm (LT), 0.27 vs. 0.27 (MCSv), and 618.2 vs. 622.1 (MU), respectively. Significant differences were observed for CLS and LT. The average γ passing rates (clinical plan vs. KBP) were as follows: 99.0% vs. 99.1% (3%/3 mm) and 92.4% vs. 92.5% (2%/2 mm) with ArcCHeck, and 99.5% vs. 99.4% (3%/3 mm) and 95.2% vs. 95.4% (2%/2 mm) with EBT3 film, respectively. CONCLUSIONS: The KBP used lower multileaf collimator (MLC) travel and more closed or small MLC apertures than the clinical plan. The KBP system of VMAT for the prostate cancer was acceptable for clinical use without any major problems.

BACKGROUND/AIM: A newly-introduced tungsten containing rubber (TCR) is a potentially useful shielding material in electron radiotherapy because it is lead-free, containing as much as 90% fine tungsten powder by weight. This study aimed to investigate the shielding ability of TCR against electron beams. MATERIALS AND METHODS: Transmission of TCR was measured for energies of 4, 6, 9 and 12 MeV. Dose profiles were measured to compare the TCR and lead. The electron backscatter factor (EBF) was also compared. RESULTS: The transmission of equivalent thickness for 4, 6, 9 and 12 MeV with TCR (0.78%, 1.34%, 2.16% and 3.08%, respectively) were lower than that with lead (0.81%, 1.44%, 2.19% and 3.16%, respectively) (p<0.05). The dose profiles were not significantly different for TCR and lead. The EBF with TCR was up to 17% lower than that with lead. CONCLUSION: TCR has adequate radiation shielding ability for electron beams and could be employed instead of lead.

Tungsten functional paper (TFP) is a paper-based radiation-shielding material, which is lead-free and easy to cut. We developed a radiation protection undergarment using TFP for prostate cancer patients treated with permanent 125I seed implantation (PSI). The aim of this study was to evaluate the shielding ability of the undergarment with respect to household contacts and members of the public. Between October 2016 and April 2017, a total of 10 prostate cancer patients treated with PSI were enrolled in this prospective study. The external radiation exposure from each patient 1 day after PSI was measured with and without the undergarment. Measurements were performed using a survey meter at 100 cm from the surface of the patient's body. The exposure rates were measured from five directions: anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior. The measured radiation exposure rates without the undergarment, expressed as mean ± standard deviation, from the anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior directions were 1.28 ± 0.43 μSv/h, 0.70 ± 0.34 μSv/h, 0.21 ± 0.062 μSv/h, 0.65 ± 0.33 μSv/h and 1.24 ± 0.41 μSv/h, respectively. The undergarment was found to have (mean ± standard deviation) shielding abilities of 88.7 ± 5.8%, 44.0 ± 42.1%, 50.6 ± 15.9%, 72.9 ± 27.0% and 90.4 ± 10.7% from the anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior directions, respectively. In conclusion, this shielding undergarment is a useful device that has the potential to reduce radiation exposure for the general public and the patient's family.

BACKGROUND: Four-dimensional computed tomography (4D-CT) ventilation is an emerging imaging modality. Functional avoidance of regions according to 4D-CT ventilation may reduce lung toxicity after radiation therapy. This study evaluated associations between 4D-CT ventilation-based dosimetric parameters and clinical outcomes. METHODS: Pre-treatment 4D-CT data were used to retrospectively construct ventilation images for 40 thoracic cancer patients retrospectively. Fifteen patients were treated with conventional radiation therapy, 6 patients with hyperfractionated radiation therapy and 19 patients with stereotactic body radiation therapy (SBRT). Ventilation images were calculated from 4D-CT data using a deformable image registration and Jacobian-based algorithm. Each ventilation map was normalized by converting it to percentile images. Ventilation-based dosimetric parameters (Mean Dose, V5 [percent lung volume receiving ≥5 Gy], and V20 [percent lung volume receiving ≥20 Gy]) were calculated for highly and poorly ventilated regions. To test whether the ventilation-based dosimetric parameters could be used predict radiation pneumonitis of ≥Grade 2, the area under the curve (AUC) was determined from the receiver operating characteristic analysis. RESULTS: For Mean Dose, poorly ventilated lung regions in the 0-30% range showed the highest AUC value (0.809; 95% confidence interval [CI], 0.663-0.955). For V20, poorly ventilated lung regions in the 0-20% range had the highest AUC value (0.774; 95% [CI], 0.598-0.915), and for V5, poorly ventilated lung regions in the 0-30% range had the highest AUC value (0.843; 95% [CI], 0.732-0.954). The highest AUC values for Mean Dose, V20, and V5 were obtained in poorly ventilated regions. There were significant differences in all dosimetric parameters between radiation pneumonitis of Grade 1 and Grade ≥2. CONCLUSIONS: Poorly ventilated lung regions identified on 4D-CT had higher AUC values than highly ventilated regions, suggesting that functional planning based on poorly ventilated regions may reduce the risk of lung toxicity in radiation therapy.

Intraoperative electron radiotherapy (IOERT), which is an accelerated partial breast irradiation method, has been used for early-stage breast cancer treatment. In IOERT, a protective disk is inserted behind the target volume to minimize the dose received by normal tissues. However, to use such a disk, the surgical incision must be larger than the field size because the disk is manufactured from stiff and unyielding materials. In this study, the applicability of newly developed tungsten-based functional paper (TFP) was assessed as an alternative to the existing protective disk. The radiation-shielding performance of the TFP was verified through experimental measurements and Monte Carlo simulations. Percentage depth dose curves and lateral dose profiles with and without TFPs were measured and simulated on a dedicated IOERT accelerator. The number of piled-up TFPs was changed from 1 to 40. In the experimental measurements, the relative doses at the exit plane of the TFPs for 9 MeV were 42.7%, 9.2%, 0.2%, and 0.1% with 10, 20, 30, and 40 TFPs, respectively, whereas those for 12 MeV were 63.6%, 27.1%, 8.6%, and 0.2% with 10, 20, 30, and 40 TFPs, respectively. Slight dose enhancements caused by backscatter radiation from the TFPs were observed at the entrance plane of the TFPs at both beam energies. The results of the Monte Carlo simulation indicated the same tendency as the experimental measurements. Based on the experimental and simulated results, the radiation-shielding performances of 30 TFPs for 9 MeV and 40 TFPs for 12 MeV were confirmed to be acceptable and close to those of the existing protective disk. The findings of this study suggest the feasibility of using TFPs as flexible chest wall protectors in IOERT for breast cancer treatment.

Pretreatment intensity-modulated radiotherapy quality assurance is performed using simple rectangular or cylindrical phantoms; thus, the dosimetric errors caused by complex patient-specific anatomy are absent in the evaluation objects. In this study, we construct a system for generating patient-specific three-dimensional (3D)-printed phantoms for radiotherapy dosimetry. An anthropomorphic head phantom containing the bone and hollow of the paranasal sinus is scanned by computed tomography (CT). Based on surface rendering data, a patient-specific phantom is formed using a fused-deposition-modeling-based 3D printer, with a polylactic acid filament as the printing material. Radiophotoluminescence glass dosimeters can be inserted in the 3D-printed phantom. The phantom shape, CT value, and absorbed doses are compared between the actual and 3D-printed phantoms. The shape difference between the actual and printed phantoms is less than 1 mm except in the bottom surface region. The average CT value of the infill region in the 3D-printed phantom is -6 ± 18 Hounsfield units (HU) and that of the vertical shell region is 126 ± 18 HU. When the same plans were irradiated, the dose differences were generally less than 2%. These results demonstrate the feasibility of the 3D-printed phantom for artificial in vivo dosimetry in radiotherapy quality assurance.

Purpose: The Vero4DRT has a maximum field size of 150×150 mm². The purposes of this study were to develop an expanded field irradiation technique using a unique gimbaled x‐ray head of Vero4DRT and to evaluate its dosimetric characteristic. Methods: The expanded field irradiation consisted of four separate fields with 2.39 degree gimbal rotation around orthogonal two axes. The central beam axis for each field shifted 40 mm from the isocenter for longitudinal and lateral directions, and thus, the field size was expanded up to 230×230 mm². Adjacent region were created at the isocenter (center‐adjacent expanded‐field) and 20 mm from isocenter (offadjacent expanded‐field). To create flat dose distribution in the combined piecewise‐fields, the overlapping and gaps regions on the isocenter plane were adjusted with the gimbal rotating and the MLC. To evaluate dosimetric characteristic of the expanded‐field, films inserted in water‐equivalent phantoms at 50, 100 and 150 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expandedfield irradiation technique was applied to IMRT. A head and neck IMRT field, which was planned for the conventional linac (Varian Clinac iX), was reproduced with the expanded‐field of the Vero4DRT. The simulated dose distribution for the expanded IMRT field was compared to the measured dose distribution. Results: The field size, penumbra, flatness and symmetry of center‐ and off‐ adjacent expanded‐fields were 230.2–232.1 mm, 7.8–10.7 mm, 2.3–6.5% and –0.5–0.4% at 100 mm depth. The 82.1% area of the expanded IMRT dose distribution was within 5% difference between measurement and simulation, which was analyzed upper 50% dose area, and the 3%/3 mm gamma pass rate was 98.4%. Conclusions: The expandedfield technique was developed using the gimbaled x‐ray head. To extend applied targets, such as whole breast irradiations or head and neck IMRT, the expanded‐field technique would be effective.

PURPOSE: The purpose of this study was to investigate the status of the implementation of quality assurance (QA) for intensity-modulated radiation therapy (IMRT) in Japan using a questionnaire survey. METHODS: The questionnaire consisted of seven sections: (1) clinical uses of IMRT, (2) treatment planning systems, treatment machines, phantoms for verification and CT scanning, (3) absorbed dose verification, (4) dose distribution verification, (5) fluence map verification, (6) acceptance criteria for each verification, and (7) comments. RESULTS: The questionnaire was completed by 129 institutions (response rate: 76.8%). IMRT was performed for prostate cancer in 125 institutions (96.9%), followed by head and neck cancer in 83 (64.3%), and brain tumors in 69 (53.5%). Although at least three individuals were engaged in IMRT QA in 77.5% of the institutions, the number of full-time persons involved in IMRT QA was one or less in 94 institutions (72.9%). This indicated that most institutions in Japan have a staff shortage. More than 90% of the institutions verified both the absorbed dose and dose distribution. The acceptance criterion for the absorbed dose verification was set to ±3% in at least 80% of the institutions. Gafchromic film was used for the majority of dose distribution verifications. The acceptance criteria for dose distribution verification mainly involved gamma analysis and a comparison of dose profiles; however, the judgment of acceptance did not depend on the results of the gamma analysis. CONCLUSION: This survey increases our understanding of how institutions currently perform IMRT QA analysis. This understanding will help to move institutions toward more standardization of IMRT QA in Japan.

Objective
The present study aimed at establishing a new protocol using both ^99mTc-Tetrofosmin (TF) and ¹²³I-BMIPP SPECT to detect myocardial damage within one hour.
Methods
Initial ¹²³I-BMIPP SPECT was immediately followed by ^99mTc-TF SPECT. The influence of ¹²³I scattered rays on ^99mTc energy windows set at 15% and 10% were measured using an RH-2 phantom. Participants in the study were patients with heart diseases who had provided written informed consent to undergo the new protocol. The patients maintained the MONZEN position throughout the procedure and an injection syringe was attached to the left arm for ^99mTc-TF injection during¹²³I-BMIPP SPECT.
Results & Discussion
The phantom study showed only slight ¹²³I contamination of ^99mTc at the 10% window setting. The new method separated the ¹²³I and ^99mTc energy windows well and neither crosstalk nor scatter correction were needed. Images obtained from dual (simultaneous) acquisition were contaminated, whereas contamination and influence of scattered rays were absent in images obtained by use of the new protocol. These images were thus useful for clinical diagnosis.
Conclusion
The new protocol is more convenient for patients and might improve the efficiency of detecting myocardial damage.

温熱治療は一般的に42.5℃以上の温度で行われている. しかし, 我々は42.5℃以下の温度による温熱治療によっても, 免疫能活性が発生し, その結果, 抗腫瘍効果の発生する事を確認した. 実験にはSCC-VII腫瘍を大腿部皮下に担癌させたC3Hマウスを用いた. 担癌マウスの大腿部に対して39℃から41℃の低温度の温熱治療を恒温水槽によって1時間加えた. 温熱処理前後の白血球数, リンパ球数, NK細胞活性を調べた. 42.5℃以下のマイルド温熱処理によって抗腫瘍効果が観測され, その腫瘍成長遅延に伴って白血球数, リンパ球数の一過性増加とNK細胞活性が観測された. これらの結果はマイルド・ハイパーサーミアによって, 免疫能が活性することを示唆している. もしも, 大腿部をマイルド・ハイパーサーミアで定量的に刺激して, 大腿部骨髄の造血器官が活性化し, 免疫能が活性化するのであれば, マイルド・ハイパーサーミアは癌治療患者に対しては癌の転移を抑える可能性があり, 更に免疫能が関与する疾患の治療 (例えばC型肝炎, 膠原病, エイズ, 術後の回復, 温熱治療時の補助治療, その他免疫不全の解消等) に有効な治療となると考えられる.

三酸化二砒素 (以下ATO) は急性前骨髄球性白血病 (APL) や他の白血病に対して効果的な抗癌剤であることが知られており, 世界の注目を浴びている.しかし, ATOの固形腫瘍に対する有用性は研究が始まって間もなく, 今後の研究が期待されている.今回, 我々はATO投与とHyperthermia を併用する順番を変えたとき, 腫瘍成長抑制効果に違いがあるかを検討した.腫瘍体積変化の結果から, 併用処理による相乗効果が見られたが, 両併用群間には腫瘍成長抑制効果に有意な差は見られなかった.また, 腫瘍病理標本上の結果からも大きな違いは見られなかった.

hyperthermiaにおいて温度を測定することは重要である. 生体の温度を測る方法として, 熱電対温度計がある. 熱電対温度計を使う問題として, 部分的な場所のみしか温度が測定できないこと, 患者を大きく侵襲することがあげられる. そのうえ, ホットスポットを知ることができない. そこで我々はコイルを使って温度を測ることを研究した.
被加温体に高周波電界をかけると, 周囲に高周波磁界を生じる. その磁界の減衰は1/ (2πr : rは距離) である. そのプロファイルから電流密度を計算した. 高周波電流と温度の上昇には相関が見られた. 実際に加温を行い, サーモグラフィで撮像したものと, 本研究によって得られた結果は相関が見られた. よって, 被加温体の電流密度を測定すれば, 非侵襲的に, 温度が測定できることがわかった.

本研究ではRI内用療法において、線量計測や線量シミュレーション手法を用いることにより、腫瘍や臓器のマクロな線量評価の手法と微小な組織の線量評価の手法を開発し、その結果を織り込んで標準的な実施指針を提案し、RI内用療法の臨床研究への導入を推進することを目的とする。第3者の被ばくについてもその手法を織り込んだ標準的な実施指針を目指している。さて新規RI内用療法の臨床応用にあたっては妥当な放射線安全のもとで治療の有効性と安全性を検証するために実施指針が求められる。新規RI内用療法が次々に開発されている現在、本研究は、正常臓器や病巣の吸収線量の評価に基づいて実施指針を作成するために、標準的なテンプレートを作成する。そのような標準的なテンプレートは同時に治療手法の最適化を図ることにも通じる。そこで線量計算ソフトを導入して体内分布データに基づいてRI内用療法患者の線量計算手法を確立した。またラジウム-223治療を実施した去勢抵抗性前立腺癌骨転移のデータを蓄積し、個別化治療の開発に繋がる因子を解析した。またルテチウムオキソドトレオチド（177Lu）を実際に症例において実施し、それによって得られた知見を新規RI内用療法における臨床応用に求められる要件に活用することができた。今後の新しいRI内用療法においては体内分布データの取得手法を開発することと、それに基づいた線量評価を実施するための手法を構築していくことが重要である。本研究の独自性と創造性については、本研究で実施している新規核種の線量評価に基づいた手法の検討は、通常の医療施設やアイソトープ研究施設では実施困難である。アルファ線核種を初めとする新規核種を使用できる設備を持っていること、また臨床医である研究代表者と放射線計測と線量分析を専門とする研究分担者が共同研究することが本研究の特徴である。

肺癌に対する根治的放射線治療において、Volumetoric Modulated Arc Therapy（VMAT）やHelical Tomotherapy（HT）は強度変調放射線治療(IMRT)の標準的な技術であるが、治療後の放射線肺臓炎（RP）が懸念される。今回、VMATあるいはHTを用いたIMRTを受けた肺癌患者において、RPと関連する要因を検討した。2018年4月～2020年12月までに60Gy/30fr/6週のIMRTを受けた肺癌52例(VMAT:31例、HT:21例)を検討した。年齢の中央値は70歳(53-85歳)、臨床病期はそれぞれⅡ期が5例、Ⅲ期が47例であり、うち11例に肺切除歴を認めた。放射線治療の開始から肺臓炎発生までの累積時間はKaplan-Meier法で算出し、放射線治療後の肺臓炎と関連する臨床的要因についてはCOX比例ハザードモデルを用いて解析を行った。観察期間中央値は14ヵ月(5～33ヵ月)、観察期間中に18例が再発、8例が死亡した。RPはGrade(G)1 : 26例、G2 : 12例、G3: 6例、G4 : 1例、G5 : 1例であった(CTCAE ver5.0)。G2以上のRPの発生は、単変量解析において計画標的体積（PTV）≧365cc、全肺のV20≧18％およびV5≧44％、Dmean≧11Gy、患側肺のV20≧36％およびV5≧61％とそれぞれ有意に関連していた（p<0.05）。しかし、多変量解析ではG2以上のRPに関連する因子は認めなかった。G3以上のRPについては、単変量解析の結果、肺切除の既往歴、全肺容積≧3150cc、全肺のV5≧44％、患側肺のV20≧36％、V5≧61％と有意に関連していた。さらに、多変量解析にて肺切除歴はG3以上のRPと有意に関連していた（p＝0.048）。

Deformable Registrationソフトウェアと4次元線量分布評価システムを開発した。また、新規に一筆書き照射法を考案し、その有用性を膵臓癌および頭蓋底腫瘍において確認した。さらに、膵臓癌において臓器移動や変形が線量分布に及ぼす影響を評価し、呼吸停止下強度変調放射線治療を開発して第一相線量増加試験を開始するとともに、悪性胸膜中皮腫および頸部食道癌に対する強度変調放射線治療を用いた臨床試験プロトコールをそれぞれ立案し実施中である。

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