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Okamoto H, Wakita A, Tani K, Kito S, Kurooka M, Kodama T, Tohyama N, Fujita Y, Nakamura S, Iijima K, Chiba T, Nakayama H, Murata M, Goka T, Igaki H. Plan complexity metrics for head and neck VMAT competition plans. Med Dosim 2024:S0958-3947(24)00009-8. [PMID: 38368182 DOI: 10.1016/j.meddos.2024.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 12/22/2023] [Accepted: 01/24/2024] [Indexed: 02/19/2024]
Abstract
Previous plan competitions have largely focused on dose metric assessments. However, whether the submitted plans were realistic and reasonable from a quality assurance (QA) perspective remains unclear. This study aimed to investigate the relationship between aperture-based plan complexity metrics (PCM) in volumetric modulated arc therapy (VMAT) competition plans and clinical treatment plans verified through patient-specific QA (PSQA). In addition, the association of PCMs with plan quality was examined. A head and neck (HN) plan competition was held for Japanese institutions from June 2019 to July 2019, in which 210 competition plans were submitted. Dose distribution quality was quantified based on dose-volume histogram (DVH) metrics by calculating the dose distribution plan score (DDPS). Differences in PCMs between the two VMAT treatment plan groups (HN plan competitions held in Japan and clinically accepted HN VMAT plans through PSQA) were investigated. The mean (± standard deviation) DDPS for the 98 HN competition plans was 158.5 ± 20.6 (maximum DDPS: 200). DDPS showed a weak correlation with PCMs with a maximum r of 0.45 for monitor unit (MU); its correlation with some PCMs was "very weak." Significant differences were found in some PCMs between plans with the highest 20% DDPSs and the remaining plans. The clinical VMAT and competition plans revealed similar distributions for some PCMs. Deviations in PCMs for the two groups were comparable, indicating considerable variability among planners regarding planning skills. The plan complexity for HN VMAT competition plans increased for high-quality plans, as shown by the dose distribution. Direct comparison of PCMs between competition plans and clinically accepted plans showed that the submitted HN VMAT competition plans were realistic and reasonable from the QA perspective. This evaluation may provide a set of criteria for evaluating plan quality in plan competitions.
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Affiliation(s)
- Hiroyuki Okamoto
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan.
| | - Akihisa Wakita
- Division of Medical Physics, EuroMediTech Co., LTD., 2-20-4 higashigotanda, shinagawa-ku Tokyo, 141-0022, Japan
| | - Kensuke Tani
- Division of Medical Physics, EuroMediTech Co., LTD., 2-20-4 higashigotanda, shinagawa-ku Tokyo, 141-0022, Japan
| | - Satoshi Kito
- Department of Radiology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku Tokyo,113-8677, Japan
| | - Masahiko Kurooka
- Department of Radiation Therapy, Tokyo Medical University Hospital, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan
| | - Takumi Kodama
- Department of Radiation Oncology, Saitama Cancer Center, 780 Ooazakomuro, Inamachi, Kitaadachi-gun Saitama 362-0806, Japan
| | - Naoki Tohyama
- Division of Medical Physics, Tokyo Bay Makuhari Clinic for Advanced Imaging, Cancer Screening, and High-Precision Radiotherapy, 1-17 Toyosuna, Mihama-ku Chiba, Chiba, 261-0024, Japan
| | - Yukio Fujita
- Department of Radiation Sciences, Komazawa University, 1-23-1, komazawa, setagaya-ku Tokyo, 154-8525, Japan
| | - Satoshi Nakamura
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Kotaro Iijima
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Takahito Chiba
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Hiroki Nakayama
- Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Miyuki Murata
- Department of Radiological Technology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Tomonori Goka
- Department of Radiological Technology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
| | - Hiroshi Igaki
- Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo, 104-0045, Japan
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Hui CB, Pourmoghaddas A, Mutaf YD. The effects of flattening filter-free beams and aperture shape controller on the complexity of conventional large-field treatment plans. J Appl Clin Med Phys 2023; 24:e14108. [PMID: 37528683 PMCID: PMC10647973 DOI: 10.1002/acm2.14108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 06/23/2023] [Accepted: 07/14/2023] [Indexed: 08/03/2023] Open
Abstract
PURPOSE The purpose of this study was to investigate the impact of using flattening filter-free (FFF) beams and the aperture shape controller (ASC) on the complexity of conventional large-field treatment plans. METHODS AND MATERIALS A total of 24 head and neck (H&N) and 24 prostate with pelvic nodes treatment plans were used in this study. Each plan was reoptimized using the original clinical objectives with both flattened and FFF beams, as well as six different ASC settings. The dosimetric qualities of each plan cohort were evaluated using commonly used dose-volume histogram values, and plan complexities were assessed through metrics including monitor unit (MU)/Dose, change in gantry speed, multileaf collimator (MLC) speed, the edge area ratio metric (EM), and the equivalent square length. RESULTS No significant differences in dosimetric qualities were found between plans with flattened and FFF beams. The ASC settings did not have significant effects on dosimetric qualities in the H&N plan cohort, but the "very high" ASC setting resulted in poorer dosimetric results for the prostate plans. Plans with FFF beams had significantly higher MU/Dose compared to plans with flattened beams. The use of flattening filter (FF) had significant effects on the change in gantry speed, with flattened beams producing plans that required higher change in gantry speed. However, the FF did not have significant effects on MLC speed, EM, or equivalent square length. In contrast, ASC settings had significant effects on these three metrics; increasing the ASC level resulted in plans with decreasing MLC speed, lower edge area ratio, and higher equivalent square length. CONCLUSION This study demonstrated that using FFF beams with various ASC settings, except for the "very high" level, can produce plans with reduced complexities without compromising dosimetric qualities in conventional large-field treatment plans.
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Affiliation(s)
- Cheukkai B. Hui
- Department of Radiation OncologyKaiser PermanenteDublinCaliforniaUSA
| | | | - Yildirim D. Mutaf
- Department of Radiation OncologyKaiser PermanenteDublinCaliforniaUSA
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Götstedt J, Karlsson A, Bäck A. Evaluation of measures related to dosimetric uncertainty of VMAT plans. J Appl Clin Med Phys 2022; 24:e13862. [PMID: 36519586 PMCID: PMC10113703 DOI: 10.1002/acm2.13862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 11/11/2022] [Accepted: 11/14/2022] [Indexed: 12/23/2022] Open
Abstract
Dosimetric uncertainty is most often not included in the process of creating and selecting plans for treatment. Treatment planning and the physician's choice of treatment plan is instead often based only on evaluation of clinical goals of the calculated absorbed dose distribution. Estimation of the dosimetric uncertainty could potentially have impact in the process of comparing and selecting volumetric modulated arc therapy (VMAT) plans. In this study, different measures for estimation of dosimetric uncertainty based on treatment plan parameters for plans with similar dose distributions were evaluated. VMAT plans with similar dose distributions but with different treatment plan designs were created using three different optimization methods for each of ten patient cases (tonsil and prostate cancer). Two plans were optimized in Eclipse, one with and one without the use of aperture shape controller, and one plan was optimized in RayStation. The studied measures related to dosimetric uncertainty of treatment plans were aperture-based complexity metric analysis, investigation of modulation level of multi leaf collimator leaves, gantry speed and dose rate, quasi-3D measurements and evaluation of simulations of realistic delivery variations. The results showed that there can be variations in dosimetric uncertainty for treatment plans with similar dose distributions. Dosimetric uncertainty assessment could therefore have impact on the choice of plan to be used for treatment and lead to a decrease in the uncertainty level of the delivered absorbed dose distribution. This study showed that aperture shape complexity had a larger impact on dosimetric uncertainty compared to modulation level of MLC, gantry speed and dose rate.
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Affiliation(s)
- Julia Götstedt
- Department of Radiation Physics Institute of Clinical Sciences Sahlgrenska Academy University of Gothenburg Gothenburg Sweden
- Department of Therapeutic Radiation Physics Medical Physics and Biomedical Engineering Sahlgrenska University Hospital Gothenburg Sweden
| | - Anna Karlsson
- Department of Radiation Physics Institute of Clinical Sciences Sahlgrenska Academy University of Gothenburg Gothenburg Sweden
- Department of Therapeutic Radiation Physics Medical Physics and Biomedical Engineering Sahlgrenska University Hospital Gothenburg Sweden
| | - Anna Bäck
- Department of Radiation Physics Institute of Clinical Sciences Sahlgrenska Academy University of Gothenburg Gothenburg Sweden
- Department of Therapeutic Radiation Physics Medical Physics and Biomedical Engineering Sahlgrenska University Hospital Gothenburg Sweden
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A measurement validation of improved plan deliverability with monitor unit objective tool for spine stereotactic ablative radiotherapy. Med Dosim 2022; 48:25-30. [PMID: 36280549 DOI: 10.1016/j.meddos.2022.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 08/25/2022] [Accepted: 09/20/2022] [Indexed: 02/04/2023]
Abstract
Spine stereotactic body radiation therapy (SBRT) uses high dose per fraction for palliative pain control. The treatment plans are often heavily modulated due to close proximity to spinal cord and this can lead to poor plan quality which are susceptible to dose delivery discrepancy. Therefore, we aim to assess the effectiveness of the monitor unit (MU) objective tool in Eclipse treatment planning systems in modulating the plan complexity to improve the plan quality in spine SBRT. Seven retrospective spine SBRT plans are re-optimized using the MU objective tool in Eclipse TPS v13.6 and were compared with the original plans. The dose metrics of the tumor PTV were compared using D1cc. D99%, D95%, D0.03cc, D0.1cc, D0.35cc and D1cc, and that of cord PRV were compared using D0.03cc, D0.1cc, D0.35cc. Four different plan complexities were also calculated for the original and re-optimized plans to quantify the impact of the tool on the modulation. Patient specific quality assurance measurements were performed with Stereophan and SRS MapCheck, and analyzed using the 1%/1-mm and 2%/2-mm criteria with gamma analysis. The dose metrics of the PTV and cord PRV of the re-optimized and original plans are similar and still meet the planning dose constraints. In particular, the PTV dose coverage has a small percentage difference of (0.15 ± 1.33)% and (0.01 ± 1.04)% for D99% and D95%, respectively. The 4 calculated plan complexity metrics consistently show that the re-optimized plans are quantitatively less complex than the original plan. The gamma passing rate of the re-optimized plans improved from (92.2 ± 2.0)% to (94.2 ± 1.6)% with the 1%/1-mm criterion, and (98.7 ± 1.0)% to (99.5 ± 0.3)% with the 2%/2-mm criterion. Overall, the re-optimized plans achieve at least a 10% MU reduction (11.7% to 24.6%). Our study shows that optimization with the MU objective tool can reduce plan complexity and improves dose delivery accuracy, while not compromising the dose distribution.
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Nakamura H, Tamamoto T, Tooyama T, Iida R, Yamamoto S, Hirohashi R. [Impact of Irradiation Field Aperture Controller Settings on Patient-specific Quality Assurance]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2022; 78:188-199. [PMID: 35185098 DOI: 10.6009/jjrt.780204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE The aperture shape controller (ASC) is a tool on a radiation therapy planning system to reduce complexity by increasing the aperture size of multileaf collimator (MLC). The purposes of this study were to clarify the effect of the dose index on the treatment plan when the intensity of ASC is changed and then to clarify the effect on the verification result in the individual patient-specific quality assurance (QA) using the verification phantom. METHODS For four types of mock structures presented at AAPM TG-119, volumetric modulated arc therapy (VMAT) treatment plans with three dose levels were set without using the ASC for each of these four types. ASC settings were changed to very low, low, moderate, high and very high for the treatment plan, and the treatment plan was recreated without changing the planning target volume (PTV) and/or OAR dose constraints. The dose index of the treatment plan was then evaluated. The plan was also transferred by the true composite method to the assessment phantom, and patient-specific QA was evaluated. RESULTS The frequency of dose constraint deviation by changing the ASC was 3.6% (2/55). In patient-specific QA, when the ASC setting was set to moderate, the γ analysis passing rate increased by 1.5% compared to the case without the ASC. In the treatment plan with a γ analysis pass rate of 95% or less without ASC, a 2.7% increase in the γ analysis pass rate was observed by setting the ASC to moderate. CONCLUSION We found that setting the ASC tended to improve patient-specific QA. Compared to when the ASC was not set, the evaluation result of patient-specific QA was improved without violating the dose constraints of the PTV and/or organ at risk (OAR). In particular, the improvement was notable for the case where the evaluation result of patient-specific QA was 95% or less when the ASC was not used.
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Affiliation(s)
- Hiroyuki Nakamura
- Department of Central Radiology, Saiseikai Suita Hospital.,Department of Radiation Oncology, Nara Medical University School of Medicine
| | - Tetsuro Tamamoto
- Department of Radiation Oncology, Nara Medical University School of Medicine.,Department of Medical Informatics, Nara Medical University Hospital
| | | | - Ryo Iida
- Department of Central Radiology, Saiseikai Suita Hospital
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Quintero P, Cheng Y, Benoit D, Moore C, Beavis A. Effect of treatment planning system parameters on beam modulation complexity for treatment plans with single-layer multi-leaf collimator and dual-layer stacked multi-leaf collimator. Br J Radiol 2021; 94:20201011. [PMID: 33882242 PMCID: PMC8173683 DOI: 10.1259/bjr.20201011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVE High levels of beam modulation complexity (MC) and monitor units (MU) can compromise the plan deliverability of intensity-modulated radiotherapy treatments. Our study evaluates the effect of three treatment planning system (TPS) parameters on MC and MU using different multi-leaf collimator (MLC) architectures. METHODS 192 volumetric modulated arc therapy plans were calculated using one virtual prostate phantom considering three main settings: (1) three TPS-parameters (Convergence; Aperture Shape Controller, ASC; and Dose Calculation Resolution, DCR) selected from Eclipse v15.6, (2) four levels of dose-sparing priority for organs at risk (OAR), and (3) two treatment units with same nominal conformity resolution and different MLC architectures (Halcyon-v2 dual-layer MLC, DL-MLC & TrueBeam single-layer MLC, SL-MLC). We use seven complexity metrics to evaluate the MC, including two new metrics for DL-MLC, assessed by their correlation with γ passing rate (GPR) analysis. RESULTS DL-MLC plans demonstrated lower dose-sparing values than SL-MLC plans (p<0.05). TPS-parameters did not change significantly the complexity metrics for either MLC architectures. However, for SL-MLC, significant variations of MU, target volume dose-homogeneity, and dose spillage were associated with ASC and DCR (p<0.05). MU were found to be correlated (highly or moderately) with all complexity metrics (p<0.05) for both MLC plans. Additionally, our new complexity metrics presented a moderate correlation with GPR (r<0.65). An important correlation was demonstrated between MC (plan deliverability) and dose-sparing priority level for DL-MLC. CONCLUSIONS TPS-parameters selected do not change MC for DL-MLC architecture, but they might have a potential use to control the MU, PTV homogeneity or dose spillage for SL-MLC. Our new DL-MLC complexity metrics presented important information to be considered in future pre-treatment quality assurance programs. Finally, the prominent dependence between plan deliverability and priority applied to OAR dose sparing for DL-MLC needs to be analyzed and considered as an additional predictor of GPRs in further studies. ADVANCES IN KNOWLEDGE Dose-sparing priority might influence in modulation complexity of DL-MLC.
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Affiliation(s)
- Paulo Quintero
- Medical Physics Service, Castle Hill Hospital, Hull University Teaching Hospitals NHS Trust, Hull, UK.,Department of Physics and Mathematics, University of Hull, Hull, UK
| | - Yongqiang Cheng
- Department of Computer Science and Technology, University of Hull, Hull, UK
| | - David Benoit
- Department of Physics and Mathematics, University of Hull, Hull, UK
| | - Craig Moore
- Medical Physics Service, Castle Hill Hospital, Hull University Teaching Hospitals NHS Trust, Hull, UK
| | - Andrew Beavis
- Medical Physics Service, Castle Hill Hospital, Hull University Teaching Hospitals NHS Trust, Hull, UK.,Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, UK.,Faculty of Health Sciences, University of Hull, Hull, UK
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Götstedt J, Bäck A. Edge area metric complexity scoring of volumetric modulated arc therapy plans. PHYSICS & IMAGING IN RADIATION ONCOLOGY 2021; 17:124-129. [PMID: 33898791 PMCID: PMC8058026 DOI: 10.1016/j.phro.2021.02.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Revised: 02/12/2021] [Accepted: 02/23/2021] [Indexed: 12/01/2022]
Abstract
Background and purpose Aperture-based complexity metrics have been suggested as a method to score complexity of volumetric modulated arc therapy (VMAT) plans. The purpose of this study was to evaluate the edge area metric (EAM) for clinical VMAT plans on a control point and treatment plan level. Materials and methods EAM on a control point level was evaluated based on film measurements of 18 static beam openings originating from VMAT plans. EAM on a treatment plan level (arithmetic mean value of EAM scores for control points) was evaluated based on measurements with the Delta4® for 200 VMAT plans for four different treatment sites: pelvic, thorax, head and neck, and prostate. Measurements were compared to calculations and dose difference and gamma pass rates were evaluated. Results EAM scores on a control point level correlated with Pearson's r-values of -0.96 and -0.77 to dose difference and gamma pass rates, respectively. The prostate plans had the highest average EAM score. A connection between smaller PTVs and higher EAM scores was found. No correlation between the evaluation result and EAM on a plan level was found. Conclusions EAM on a control point level was shown to correlate to the difference between measured and calculated 2D dose distributions of clinical VMAT beam openings. No correlation was found for EAM on a plan level for clinical treatment plans.
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Affiliation(s)
- Julia Götstedt
- Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden
| | - Anna Bäck
- Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden.,Department of Therapeutic Radiation Physics, Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, 413 45 Gothenburg, Sweden
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Ito T, Tamura M, Monzen H, Matsumoto K, Nakamatsu K, Harada T, Fukui T. [Impact of Aperture Shape Controller on Knowledge-based VMAT Planning of Prostate Cancer]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2021; 77:23-31. [PMID: 33473076 DOI: 10.6009/jjrt.2021_jsrt_77.1.23] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
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.
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Affiliation(s)
- Takaaki Ito
- Department of Radiological Technology, Kobe City Nishi-Kobe Medical Center
| | - Mikoto Tamura
- Department of Medical Physics, Graduate School of Medical Sciences, Kindai University
| | - Hajime Monzen
- Department of Medical Physics, Graduate School of Medical Sciences, Kindai University
| | - Kenji Matsumoto
- Department of Medical Physics, Graduate School of Medical Sciences, Kindai University.,Department of Radiology, Kindai University Hospital
| | - Kiyoshi Nakamatsu
- Department of Radiation Oncology, Faculty of Medicine, Kindai University
| | - Tomoko Harada
- Department of Radiological Technology, Kobe City Nishi-Kobe Medical Center
| | - Tatsuya Fukui
- Department of Radiological Technology, Kobe City Nishi-Kobe Medical Center
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The use of aperture shape controller and convergence mode in radiotherapy treatment planning. JOURNAL OF RADIOTHERAPY IN PRACTICE 2020. [DOI: 10.1017/s1460396920001028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Abstract
Aim:
Studying the use of Aperture Shape Controller (ASC) and Convergence Mode (CM) in Eclipse (Varian Medical System) in terms of plan quality and complexity of volumetric modulated arc therapy (VMAT).
Materials and methods:
Forty VMAT plans were re-optimised for the prostate, prostate + lymph nodes, breast and head & neck patients retrospectively, changing the ASC settings (off, moderate, very high) and CM settings (off, on and extended).
Results:
Using ‘on’ or ‘extended’ CM increased plan quality in terms of planning target volume homogeneity and low-dose spread to the organs at risk (OAR). ‘Extended’ CM increased the optimisation time 4·3-fold compared to ‘on’, and deteriorated the plan quality in several simple planning cases. ‘Moderate’ ASC decreased plan complexity with minor effect on plan quality compared to ‘off’, but ‘very high’ ASC had larger adverse dosimetric effects. However, the ASC decreased the plan complexity only if the CM was turned ‘on’.
Findings:
Using ‘on’ CM increases the plan quality but using ‘extended’ CM is not recommended. The ‘moderate’ ASC decreased complexity without significant adverse effects on plan quality, and even ‘very high’ ASC may be used when plan simplicity is prioritised. However, if CM is not used, the ASC should also be turned off.
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