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  • Original Article 2020-12-31 2020-12-31 \ 1 \ 1122 \ 366

    Linear Energy Transfer Dependence Correction of Spread-Out Bragg Peak Measured by EBT3 Film for Dynamically Scanned Proton Beams

    Moonhee Lee1 , Sunghwan Ahn2 , Wonjoong Cheon1* , Youngyih Han1,2

    https://doi.org/10.14316/pmp.2020.31.4.135

    Abstract
    Purpose: Gafchromic films for proton dosimetry are dependent on linear energy transfers (LETs), resulting in dose underestimation for high LETs. Despite efforts to resolve this problem for singleenergy beams, there remains a need to do so for multi-energy beams. Here, a bimolecular reaction model was applied to correct the under-response of spread-out Bragg peaks (SOBPs).
    Methods: For depth-dose measurements, a Gafchromic EBT3 film was positioned in water perpendicular to the ground. The gantry was rotated at 15° to avoid disturbances in the beam path. A set of films was exposed to a uniformly scanned 112-MeV pristine proton beam with six different dose intensities, ranging from 0.373 to 4.865 Gy, at a 2-cm depth. Another set of films was irradiated with SOBPs with maximum energies of 110, 150, and 190 MeV having modulation widths of 5.39, 4.27, and 5.34 cm, respectively. The correction function was obtained using 150.8-MeV SOBP data. The LET of the SOBP was then analytically calculated. Finally, the model was validated for a uniform cubic dose distribution and compared with multilayered ionization chamber data.
    Results: The dose error in the plateau region was within 4% when normalized with the maximum dose. The discrepancy of the range was <1 mm for all measured energies. The highest errors occurred at 70 MeV owing to the steep gradient with the narrowest Bragg peak.
    Conclusions: With bimolecular model-based correction, an EBT3 film can be used to accurately verify the depth dose of scanned proton beams and could potentially be used to evaluate the depth-dose distribution for patient plans.
  • Original Article 2020-12-31 2020-12-31 \ 2 \ 1138 \ 331

    High-Dose-Rate Electron-Beam Dosimetry Using an Advanced Markus Chamber with Improved IonRecombination Corrections

    Dong Hyeok Jeong , Manwoo Lee , Heuijin Lim , Sang Koo Kang , Kyoung Won Jang

    https://doi.org/10.14316/pmp.2020.31.4.145

    Abstract
    Purpose: In ionization-chamber dosimetry for high-dose-rate electron beams一above 20 mGy/pulse一the ion-recombination correction methods recommended by the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) are not appropriate, because they overestimate the correction factor. In this study, we suggest a practical ion-recombination correction method, based on Boag’s improved model, and apply it to reference dosimetry for electron beams of about 100 mGy/pulse generated from an electron linear accelerator (LINAC).
    Methods: This study employed a theoretical model of the ion-collection efficiency developed by Boag and physical parameters used by Laitano et al. We recalculated the ion-recombination correction factors using two-voltage analysis and obtained an empirical fitting formula to represent the results. Next, we compared the calculated correction factors with published results for the same calculation conditions. Additionally, we performed dosimetry for electron beams from a 6 MeV electron LINAC using an Advanced Markus® ionization chamber to determine the reference dose in water at the source-to-surface distance (SSD)=100 cm, using the correction factors obtained in this study.
    Results: The values of the correction factors obtained in this work are in good agreement with the published data. The measured dose-per-pulse for electron beams at the depth of maximum dose for SSD=100 cm was 115 mGy/pulse, with a standard uncertainty of 2.4%. In contrast, the ks values determined using the IAEA and AAPM methods are, respectively, 8.9% and 8.2% higher than our results.
    Conclusions: The new method based on Boag’s improved model provides a practical method of determining the ion-recombination correction factors for high dose-per-pulse radiation beams up to about 120 mGy/pulse. This method can be applied to electron beams with even higher doseper-pulse, subject to independent verification.
  • Original Article 2020-12-31 2020-12-31 \ 0 \ 1114 \ 367

    Dosimetric Evaluation of an Automatically Converted Radiation Therapy Plan between Radixact Machines

    Mi Young Lee1,3 , Dae Gyu Kang1 , Jin Sung Kim2,3

    https://doi.org/10.14316/pmp.2020.31.4.153

    Abstract
    Purpose: We aim to evaluate the accuracy and effectiveness of an automatically converted radiation therapy plan between Radixact machines by comparing the original plan with the transferred plan.
    Methods: The study involved a total of 20 patients for each randomly selected treatment site who received radiation treatment with Radixact. We set up the cheese phantom (Gammex RMI, Middleton, WI, USA) with an Exradin A1SL ion chamber (Standard Imaging, Madison, WI, USA) and GAFCHROMIC EBT3 film (International Specialty Products, Wayne, NJ, USA) inserted. We used three methods to evaluate an automatically converted radiation therapy plan using the features of the Plan transfer. First, we evaluated and compared Planning target volume (PTV) coverage (homogeneity index, HI; conformity index, CI) and organs at risk (OAR) dose statistics. Second, we compared the absolute dose using an ion chamber. Lastly, we analyzed gamma passing rates using film.
    Results: Our results showed that the difference in PTV coverage was 1.72% in HI and 0.17% in CI, and majority of the difference in OAR was within 1% across all sites. The difference (%) in absolute dose values was averaging 0.74%. In addition, the gamma passing rate was 99.64% for 3%/3 mm and 97.08% for 2%/2 mm.
    Conclusions: The Plan transfer function can be reliably used in appropriate situations.
  • Original Article 2020-12-31 2020-12-31 \ 3 \ 1173 \ 352

    Improvement of Calculation Accuracy in the Electron Monte Carlo Algorithm with Optional Air Profile Measurements

    Jiwon Sung1 , Hyeongmin Jin1 , Jeongho Kim1 , Jong Min Park1,2,3,4 , Jung-in Kim1,2,3 , Chang Heon Choi1,2,3 , Minsoo Chun1,2,3

    https://doi.org/10.14316/pmp.2020.31.4.163

    Abstract
    Purpose: In this study, the accuracies of electron Monte Carlo (eMC) calculation algorithms were evaluated to determine whether electron beams were modeled by optional air profiles (APs) designed for each applicator size.
    Methods: Electron beams with the energies of 6, 9, 12, and 16 MeV for VitalBeam (Varian Medical System, Palo Alto, CA, USA) and 6, 9, 12, 16, and 20 MeV for Clinac iX (Varian Medical System) were used. Optional APs were measured at the source-to-detector distance of 95 cm with jaw openings appropriate for each machine, electron beam energy, and applicator size. The measured optional APs were postprocessed and converted into the w2CAD format. Then, the electron beams were modeled and calculated with and without optional APs. Measured profiles, percentage depth doses, penumbras with respect to each machine, and energy were compared to calculated dose distributions.
    Results: For VitalBeam, the profile differences between the measurement and calculation were reduced by 0.35%, 0.15%, 0.14%, and 0.38% at 6, 9, 12, and 16 MeV, respectively, when the beams were modeled with APs. For Clinac iX, the differences were decreased by 0.16%, -0.31%, 0.94%, 0.42%, and 0.74%, at 6, 9, 12, 16, and 20 MeV, respectively, with the insertion of APs. Of note, no significant improvements in penumbra and percentage depth dose were observed, although the beam models were configured with APs.
    Conclusions: The accuracy of the eMC calculation can be improved in profiles when electron beams are modeled with optional APs.
  • Original Article 2020-12-31 2020-12-31 \ 0 \ 826 \ 286

    Structure of an Oncology Information System Based on a Cost-Effective Relational Database for Small Departments of Radiation Oncology

    Hosang Jeon1 , Dong Woon Kim1 , Ji Hyeon Joo1 , Yongkan Ki2 , Wontaek Kim2 , Dahl Park3 , Jiho Nam3 , Dong Hyeon Kim3

    https://doi.org/10.14316/pmp.2020.31.4.172

    Abstract
    Purpose: Radiation oncology information systems (ROIS) have evolved toward connecting and integrating information between radiation treatment procedures. ROIS can play an important role in utilizing modern radiotherapy techniques that have high complexity and require a large amount of information.
    Methods: Using AccessTM software, we have developed a relational database that is highly optimized for a radiotherapeutic workflow.
    Results: The prescription table was chosen as the core table to which the other tables were connected, and three types of forms-charts, worklists, and calendars- were suggested. A fast and reliable channel for delivering orders and remarks according to changes in the situation was also designed.
    Conclusions: We expect our ROIS design to inspire those who need to develop and manage an individual ROIS suitable for their radiation oncology departments at a low cost.
  • Original Article 2020-12-31 2020-12-31 \ 0 \ 1273 \ 346

    Dosimetric Comparison of Noncoplanar and Coplanar Volumetric Modulated Arc Therapy Plans for Esophageal Cancer

    So-Yeon Park

    https://doi.org/10.14316/pmp.2020.31.4.179

    Abstract
    Purpose: We compared noncoplanar volumetric modulated arc therapy (ncVMAT) plans to coplanar VMAT (cVMAT) plans by evaluating the dosimetric quality of each for esophageal cancer.
    Methods: Twenty patients treated for esophageal cancer with the cVMAT technique were retrospectively selected. The cVMAT plans consisted of three coplanar full arc beams. The ncVMAT plans consisted of two coplanar full arc beams and one noncoplanar partial arc beam ranging from 45° to 315° with a couch rotation angle of 315°±5°. For dosimetric evaluation, the dose-volumetric (DV) parameters of the planning target volume (PTV) and organs at risk (OARs) were calculated for all VMAT plans.
    Results: No clinically noticeable differences between the cVMAT and ncVMAT plans were observed in the DV parameters of the PTV. For the lungs, the VM13 Gy and mean dose for ncVMAT plans were smaller than those for cVMAT plans, showing statistically significant differences. For the heart, the values of the maximum dose for cVMAT and ncVMAT plans were 53.8±2.9 and 50.9±3.3 Gy, respectively (P=0.004). For the spinal cord, the values of the maximum dose for cVMAT and ncVMAT plans were 37.1±5.1 and 34.7±5.7 Gy, respectively (P<0.001).
    Conclusions: The use of ncVMAT plans provides better PTV coverage and sparing of OARs compared to that of cVMAT plans for long, tube-like esophageal cancer. For esophageal cancer, the ncVMAT plans showed a more favorable plan quality than the cVMAT plans.
  • Technical Note 2020-12-31 2020-12-31 \ 0 \ 1015 \ 282

    Characteristics of Magnetic Resonance-Based Attenuation Correction Map on Phantom Study in Positron Emission Tomography/Magnetic Resonance Imaging System

    Cheolpyo Hong

    https://doi.org/10.14316/pmp.2020.31.4.189

    Abstract
    An MR-based attenuation correction (MRAC) map plays an important role in quantitative positron emission tomography (PET) image evaluation in PET/magnetic resonance imaging (MRI) systems. However, the MRAC map is affected by the magnetic field inhomogeneity of MRIs. This study aims to evaluate the characteristics of MRAC maps of physical phantoms on PET/MRI images. Phantom measurements were performed using the Siemens Biograph mMR. The modular type physical phantoms that provide assembly versatility for phantom construction were scanned in a fourchannel Body Matrix coil. The MRAC map was generated using the two-point Dixon-based segmentation method for whole-body imaging. The modular phantoms were scanned in compact and non-compact assembly configurations. In addition, the phantoms were scanned repeatedly to generate MRAC maps. The acquired MRAC maps show differently assigned values for void areas. An incorrect assignment of a void area was shown on a locally compact space between phantoms. The assigned MRAC values were distorted using a wide field-of-view (FOV). The MRAC values also differed after repeated scans. However, the erroneous MRAC values appeared outside of phantom, except for a large FOV. The MRAC map of the phantom was affected by phantom configuration and the number of scans. A quantitative study using a phantom in a PET/MRI system should be performed after evaluation of the MRAC map characteristics.
  • Technical Note 2020-12-31 2020-12-31 \ 7 \ 1241 \ 388

    Trend Analysis on Korean and International Management for Activated Material Waste from Medical Linear Accelerator

    Na Hye Kwon1 , Young Jae Jang2,4 , Dong Wook Kim1 , Dong Oh Shin3 , Kum Bae Kim4 , Jin Sung Kim1 , Sang Hyoun Choi4

    https://doi.org/10.14316/pmp.2020.31.4.194

    Abstract
    This study investigated and analyzed the Korean and international status of radioactive waste management for medical linear accelerators (linacs) and proceed prior research to suggest radiation safety regulations and guidelines for the safe use of radiation. We analyzed the number of linacs installed in the radiation oncology departments of 103 institutions. In addition, we analyzed the procedures and standards for disposal in Korea and foreign countries. For foreign countries, we analyzed the status based on reports from the United States, Japan, Europe, and Canada. A total of 182 linacs are installed in Korea and 95% of them use more than 10 MV of energy. In Korea, standards for managing radioactive waste from a linac, disposal procedures, and clearance criteria have yet to be established. Therefore, radioactive waste is disposed of in different ways depending on the hospitals where they originate. Japan, the US, and Canada have recommended clearance levels and procedures for linacs. Other countries have provided management guidelines for research or large-scale accelerators, but not for medical purposes. In this study, we investigated the management of radioactive waste from medical linacs in Korea and abroad. Several foreign countries have suggested a clearance level and criteria for disposing of waste storage drums. For the safe management of medical linacs, it is necessary to establish safety management regulations. In Korea, standards for disposal, such as radiation or dose limits, are required for medical linacs. A system for clearance when disposing at a medical institution should be created.
Korean Society of Medical Physics

Vol.35 No.1
2020-12-31

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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