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Moktan H, Jiang H, Li HH, Guida K. Impact of enhanced leaf model on dose calculation accuracy in single-isocenter multitarget stereotactic radiosurgery treatments. J Appl Clin Med Phys 2025:e70039. [PMID: 39971711 DOI: 10.1002/acm2.70039] [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: 10/07/2024] [Revised: 01/15/2025] [Accepted: 02/07/2025] [Indexed: 02/21/2025] Open
Abstract
PURPOSE Single-isocenter multitarget (SIMT) radiosurgery has become increasingly popular as advancement in planning and delivery systems have made this approach clinically viable. With targets varying in size and distance from isocenter, SIMT plans are highly complex with dynamic multileaf collimator (MLC) motion. Our department recently commissioned Eclipse Treatment Planning System v18.0, which included a novel enhanced leaf model (ELM) for photon dose calculation. ELM represents the biggest update in MLC modeling on a commercial treatment planning system over the past decade, yielding improvements in leaf modeling and ray tracing. Considering its dependence on dynamic MLC movements, we set out to assess the potential clinical impact of ELM on SIMT. METHODS Dynamic zebra crosswalk (DZC) plans were delivered on a Varian Edge to investigate ELM. DZCs consisted of sweeping MLC gaps (ranging 1-15 mm) across a 3 cm width at isocenter, 4 cm, 8 cm, and 12 cm along the x-axis. Phantom dose calculations were performed using AAA v15.6 and v18.0 (with ELM) for 6 MV flattening filter free DZC plans and compared to measurements using stereotactic radiosurgery MapCHECK (Sun Nuclear Corporation) and Gafchromic EBT4 films (Ashland). To assess potential impact on SIMT, ten patients were retrospectively planned with RapidArc and HyperArc. Both versions of AAA were used for dose calculation. RESULTS DZC measurements showed improved agreement with ELM; differences between measured and calculated doses were reduced by as much as 19% for the smallest sweeping gaps at off-axis distances. Differences in central profile dose for DZCs increased with reduced gap size and increased off-axis position. SIMT plans showed up to 4.0% increase in planning target volume (PTV) maximum dose when switching from AAA v15.6 to v18.0. CONCLUSION Dose calculations with ELM mirrored diode and film measurements for highly modulated SIMT plans. ELM represents a major improvement in MLC modeling that more accurately reflects current treatment delivery practice.
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Affiliation(s)
- Hem Moktan
- Department of Radiation Oncology, University of Kansas Cancer Center, Kansas City, Kansas, USA
- Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Hongyu Jiang
- Department of Radiation Oncology, University of Kansas Cancer Center, Kansas City, Kansas, USA
| | - H Harold Li
- Department of Radiation Oncology, University of Kansas Cancer Center, Kansas City, Kansas, USA
| | - Kenny Guida
- Department of Radiation Oncology, University of Kansas Cancer Center, Kansas City, Kansas, USA
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2
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Panagi R, Caines R, Rowbottom CG. Dosimetric sensitivity of an enhanced leaf model (ELM) for individual versus averaged machines. J Appl Clin Med Phys 2025:e14621. [PMID: 39902660 DOI: 10.1002/acm2.14621] [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: 09/19/2024] [Accepted: 11/25/2024] [Indexed: 02/06/2025] Open
Abstract
BACKGROUND With the introduction of a new multi-leaf collimator (MLC) enhanced leaf model (ELM) in the Varian Eclipse™ treatment planning system, there is currently limited data regarding the dosimetric sensitivity to real-world variation in the ELM parameters, and its clinical relevance. PURPOSE To characterize the variation in ELM parameters across a large department with ten linear accelerators and investigate the feasibility of using a single machine-averaged ELM for treatment planning. This could achieve time and resource savings from reduced quality assurance, while allowing easy transfer of patients between machines. METHODS Clinical plans of a range of sites (head and neck, prostate, breast, lung, and brain), techniques (VMAT, IMRT, SBRT, and SRS), and energies (6 MV, 6 MV FFF, 10 MV, and 10 MV FFF) were recalculated on Varian TrueBeam™ (120 MLC) and Varian EDGE™ (HD120 MLC), with machine-specific ELM beam models, an averaged machine and an outlier machine model. A range of clinically relevant metrics relating to target coverage (e.g. PTV D98%, D50%, D2%) and OAR doses (dosimetric, volumetric, conformity, and gradient indices) were evaluated. RESULTS For the target metrics, the maximum percentage deviation from the mean was 0.422%, 0.157%, and 1.956% for the cases of the individual machines, the averaged machine and the outlier machine correspondingly, while the maximum absolute dose differences were 0.28 Gy, 0.07 Gy, and 0.38 Gy. For the OAR metrics, the maximum deviation from the mean was 1.833%, 0.204%, and 5.722% for the individual, averaged, and outlier machines, while the maximum absolute dose differences were 0.41 Gy, 0.10 Gy, and 0.97 Gy. CONCLUSIONS For machines that are well matched in terms of dosimetry for transmission and sweeping gap fields, the use of an averaged machine model is unlikely to introduce clinically significant dosimetric differences to treatment plans.
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Affiliation(s)
- Rafail Panagi
- Medical Physics Department, The Clatterbridge Cancer Centre NHS Foundation Trust, Liverpool, UK
| | - Rhydian Caines
- Medical Physics Department, The Clatterbridge Cancer Centre NHS Foundation Trust, Liverpool, UK
| | - Carl G Rowbottom
- Medical Physics Department, The Clatterbridge Cancer Centre NHS Foundation Trust, Liverpool, UK
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3
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Tahmasbi M, Capela M, Santos T, Mateus J, Ventura T, do Carmo Lopes M. Particular issues to be considered in small field dosimetry for TrueBeam STx commissioning. Appl Radiat Isot 2023; 202:111066. [PMID: 37865066 DOI: 10.1016/j.apradiso.2023.111066] [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: 11/09/2022] [Revised: 08/28/2023] [Accepted: 10/05/2023] [Indexed: 10/23/2023]
Abstract
This study aims to report the relevant issues concerning small fields in the commissioning of a TrueBeam STx for photon energies of 6MV, 10MV, 6FFF, and 10FFF. Percent depth doses, profiles, and field output factors were measured according to the beam model configuration of the treatment planning system. Multiple detectors were used based on the IAEA TRS-483 protocol as well as EBT3 radiochromic film. Analytical Anisotropic and Acuros XB algorithms, were configured and validated through basic dosimetry comparisons and end-to-end clinical tests.
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Affiliation(s)
- Marziyeh Tahmasbi
- Radiologic Technology Department, School of Allied Medical Sciences, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran; Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal.
| | - Miguel Capela
- Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal
| | - Tania Santos
- Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal
| | - Josefina Mateus
- Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal
| | - Tiago Ventura
- Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal
| | - Maria do Carmo Lopes
- Medical Physics Department, Instituto Portugues de Oncologia Coimbra Francisco Gentil, E.P.E., Portugal
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Passal V, Barreau M, Tiplica T, Dufreneix S. Optimizing the effective spot size and the dosimetric leaf gap of the AcurosXB algorithm for VMAT treatment planning. J Appl Clin Med Phys 2021; 22:154-161. [PMID: 34042259 PMCID: PMC8200512 DOI: 10.1002/acm2.13256] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 03/10/2021] [Accepted: 03/31/2021] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The aim of this study is to provide and test a new methodology to adjust the AcurosXB beam model for VMAT treatment plans. METHOD The effective target spot size of the AcurosXB v15 algorithm was adjusted in order to minimize the difference between calculated and measured penumbras. The dosimetric leaf gap (DLG) was adjusted using the asynchronous oscillating sweeping gap tests defined in the literature and the MLC transmission was measured. The impact of the four parameters on the small field output factors was assessed using a design of experiment methodology. Patient quality controls were performed for the three beam models investigated including two energies and two MLC models. RESULTS Effective target spot sizes differed from the manufacturer recommendations and strongly depended on the MLC model considered. DLG values ranged from 0.7 to 2.3 mm and were found to be larger than the ones based on the sweeping gap tests. All parameters were found to significantly influence the calculated output factors, especially for the 0.5 cm × 0.5 cm field size. Interactions were also identified for fields smaller than 2 cm × 2 cm, suggesting that adjusting the parameters on the small field output factors should be done with caution. All patient quality controls passed the universal action limit of 90%. CONCLUSION The methodology provided is simple to implement in clinical practice. It was validated for three beam models covering a large variety of treatment types and localizations.
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Affiliation(s)
- V. Passal
- Institut de Cancérologie de l’OuestAngersFrance
| | - M. Barreau
- LARIS Systems Engineering Research LaboratoryUniversity of AngersAngersFrance
| | - T. Tiplica
- LARIS Systems Engineering Research LaboratoryUniversity of AngersAngersFrance
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Tani K, Wakita A, Tohyama N, Fujita Y, Kito S, Miyasaka R, Mizuno N, Uehara R, Takakura T, Miyake S, Shinoda K, Oka Y, Saito Y, Kojima H, Hayashi N. Evaluation of differences and dosimetric influences of beam models using golden and multi-institutional measured beam datasets in radiation treatment planning systems. Med Phys 2020; 47:5852-5871. [PMID: 32969046 DOI: 10.1002/mp.14493] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 08/19/2020] [Accepted: 09/08/2020] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The beam model in radiation treatment planning systems (RTPSs) plays a crucial role in determining the accuracy of calculated dose distributions. The purpose of this study was to ascertain differences in beam models and their dosimetric influences when a golden beam dataset (GBD) and multi-institution measured beam datasets (MBDs) are used for beam modeling in RTPSs. METHODS The MBDs collected from 15 institutions, and the MBDs' beam models, were compared with a GBD, and the GBD's beam model, for Varian TrueBeam linear accelerator. The calculated dose distributions of the MBDs' beam models were compared with those of the GBD's beam model for simple geometries in a water phantom. Calculated dose distributions were similarly evaluated in volumetric modulated arc therapy (VMAT) plans for TG-119 C-shape and TG-244 head and neck, at several dose constraints of the planning target volumes (PTVs), and organs at risk. RESULTS The agreements of the MBDs with the GBD were almost all within ±1%. The calculated dose distributions for simple geometries in a water phantom also closely corresponded between the beam models of GBD and MBDs. Nevertheless, there were considerable differences between the beam models. The maximum differences between the mean energy of the energy spectra of GBD and MBDs were -0.12 MeV (-10.5%) in AcurosXB (AXB, Eclipse) and 0.11 MeV (7.7%) in collapsed cone convolution (CCC, RayStation). The differences in the VMAT calculated dose distributions varied for each dose region, plan, X-ray energy, and dose calculation algorithm. The ranges of the differences in the dose constraints were -5.6% to 3.0% for AXB and -24.1% to 2.8% for CCC. In several VMAT plans, the calculated dose distributions of GBD's beam model tended to be lower in high-dose regions and higher in low-dose regions than those of the MBDs' beam models. CONCLUSIONS We found that small differences in beam data have large impacts on the beam models, and on calculated dose distributions in clinical VMAT plan, even if beam data correspond within ±1%. GBD's beam model was not a representative beam model. The beam models of GBD and MBDs and their calculated dose distributions under clinical conditions were significantly different. These differences are most likely due to the extensive variation in the beam models, reflecting the characteristics of beam data. The energy spectrum and radial energy in the beam model varied in a wide range, even if the differences in the beam data were <±1%. To minimize the uncertainty of the calculated dose distributions in clinical plans, it was best to use the institutional MBD for beam modeling, or the beam model that ensures the accuracy of calculated dose distributions.
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Affiliation(s)
- Kensuke Tani
- Division of Medical Physics, EuroMediTech Co., LTD., Shinagawa, Tokyo, 141-0022, Japan
| | - Akihisa Wakita
- Division of Medical Physics, EuroMediTech Co., LTD., Shinagawa, Tokyo, 141-0022, Japan
| | - Naoki Tohyama
- Division of Medical Physics, Tokyo Bay Advanced Imaging and Radiation Oncology Makuhari Clinic, Chiba, Chiba, 261-0024, Japan
| | - Yukio Fujita
- Department of Health Sciences, Komazawa University, Setagaya, Tokyo, 154-8525, Japan
| | - Satoshi Kito
- Department of Radiotherapy, Tokyo Metropolitan Bokutoh Hospital, Sumida, Tokyo, 130-8575, Japan.,Division of Medical Physics, Graduate School of Medicine, Kyoto University, Sakyo, Kyoto, 606-8507, Japan
| | - Ryohei Miyasaka
- Department of Radiation Oncology, Chiba Cancer Center, Chiba, Chiba, 260-8717, Japan
| | - Norifumi Mizuno
- Department of Radiation Oncology, St. Luke's International Hospital, Chuo, Tokyo, 104-8560, Japan
| | - Ryuzo Uehara
- Department of Radiation Oncology, National Cancer Center Hospital East, Kashiwa, Chiba, 277-8577, Japan
| | - Toru Takakura
- Department of Radiation Oncology, Uji-Tokushukai Medical Center, Uji, Kyoto, 611-0041, Japan
| | - Shunsuke Miyake
- Department of Radiation Oncology, Yamato Takada Municipal Hospital, Yamatotakada, Nara, 635-8501, Japan
| | - Kazuya Shinoda
- Department of Radiation Oncology, Ibaraki Prefectural Central Hospital, Kasama, Ibaraki, 309-1793, Japan
| | - Yoshitaka Oka
- Department of Radiation Oncology, Fukushima Medical University Hospital, Fukushima, Fukushima, 960-1295, Japan
| | - Yasunori Saito
- Department of Radiology, Fujita Health University Hospital, Toyoake, Aichi, 470-1192, Japan
| | - Hideki Kojima
- Department of Radiation Oncology, Sapporo Higashi Tokushukai Hospital, Sapporo, Hokkaido, 065-0033, Japan
| | - Naoki Hayashi
- School of Medical Sciences, Fujita Health University, Toyoake, Aichi, 470-1192, Japan
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Rose MS, Tirpak L, Van Casteren K, Zack J, Simon T, Schoenfeld A, Simon W. Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance. Med Phys 2020; 47:3153-3164. [DOI: 10.1002/mp.14153] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 02/20/2020] [Accepted: 03/12/2020] [Indexed: 12/31/2022] Open
Affiliation(s)
- Mark S. Rose
- Sun Nuclear Corporation 3275 Suntree Blvd Melbourne Florida 32940 USA
| | - Lena Tirpak
- Sun Nuclear Corporation 3275 Suntree Blvd Melbourne Florida 32940 USA
| | | | - Jeff Zack
- Sun Nuclear Corporation 3275 Suntree Blvd Melbourne Florida 32940 USA
| | - Tom Simon
- Sun Nuclear Corporation 3275 Suntree Blvd Melbourne Florida 32940 USA
| | | | - William Simon
- Sun Nuclear Corporation 3275 Suntree Blvd Melbourne Florida 32940 USA
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Yu L, Kairn T, Trapp J, Crowe SB. Technical note: A modified gamma evaluation method for dose distribution comparisons. J Appl Clin Med Phys 2019; 20:193-200. [PMID: 31282112 PMCID: PMC6612697 DOI: 10.1002/acm2.12606] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 01/25/2019] [Accepted: 02/20/2019] [Indexed: 11/09/2022] Open
Abstract
Purpose In this work we have developed a novel method of dose distribution comparison, the inverse gamma (IG) evaluation, by modifying the commonly used gamma evaluation method. Methods The IG evaluation calculates the gamma criteria (dose difference criterion, ΔD, or distance‐to‐agreement criterion, Δd) that are needed to achieve a predefined pass rate or gamma agreement index (GAI). In‐house code for evaluating IG with a fixed ΔD of 3% was developed using Python (v3.5.2) and investigated using treatment plans and measurement data from 25 retrospective patient specific quality assurance tests (53 individual arcs). Results It was found that when the desired GAI was set to 95%, approximately three quarters of the arcs tested were able to achieve Δd within 1 mm (mean Δd: 0.7 ± 0.5 mm). The mean Δd required in order for all points to pass the gamma evaluation (i.e., GAI = 100%) was 4.5 ± 3.1 mm. The possibility of evaluating IG by fixing the Δd or ΔD/Δd, instead of fixing the ΔD at 3%, was also investigated. Conclusion The IG method and its indices have the potential to be implemented clinically to quantify the minimum dose and distance criteria based on a specified GAI. This method provides additional information to augment standard gamma evaluation results during patient specific quality assurance testing of individual treatment plans. The IG method also has the potential to be used in retrospective audits to determine an appropriate set of local gamma criteria and action levels based on a cohort of patient specific quality assurance plans.
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Affiliation(s)
- Liting Yu
- Royal Brisbane & Women's Hospital, Herston, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
| | - Tanya Kairn
- Royal Brisbane & Women's Hospital, Herston, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
| | - Jamie Trapp
- Queensland University of Technology, Brisbane, QLD, Australia
| | - Scott B Crowe
- Royal Brisbane & Women's Hospital, Herston, QLD, Australia.,Queensland University of Technology, Brisbane, QLD, Australia
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Tani K, Fujita Y, Wakita A, Miyasaka R, Uehara R, Kodama T, Suzuki Y, Aikawa A, Mizuno N, Kawamori J, Saitoh H. Density scaling of phantom materials for a 3D dose verification system. J Appl Clin Med Phys 2018; 19:103-113. [PMID: 29785725 PMCID: PMC6036349 DOI: 10.1002/acm2.12357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 02/21/2018] [Accepted: 04/05/2018] [Indexed: 12/18/2022] Open
Abstract
In this study, the optimum density scaling factors of phantom materials for a commercially available three‐dimensional (3D) dose verification system (Delta4) were investigated in order to improve the accuracy of the calculated dose distributions in the phantom materials. At field sizes of 10 × 10 and 5 × 5 cm2 with the same geometry, tissue‐phantom ratios (TPRs) in water, polymethyl methacrylate (PMMA), and Plastic Water Diagnostic Therapy (PWDT) were measured, and TPRs in various density scaling factors of water were calculated by Monte Carlo simulation, Adaptive Convolve (AdC, Pinnacle3), Collapsed Cone Convolution (CCC, RayStation), and AcurosXB (AXB, Eclipse). Effective linear attenuation coefficients (μeff) were obtained from the TPRs. The ratios of μeff in phantom and water ((μeff)pl,water) were compared between the measurements and calculations. For each phantom material, the density scaling factor proposed in this study (DSF) was set to be the value providing a match between the calculated and measured (μeff)pl,water. The optimum density scaling factor was verified through the comparison of the dose distributions measured by Delta4 and calculated with three different density scaling factors: the nominal physical density (PD), nominal relative electron density (ED), and DSF. Three plans were used for the verifications: a static field of 10 × 10 cm2 and two intensity modulated radiation therapy (IMRT) treatment plans. DSF were determined to be 1.13 for PMMA and 0.98 for PWDT. DSF for PMMA showed good agreement for AdC and CCC with 6 MV x ray, and AdC for 10 MV x ray. DSF for PWDT showed good agreement regardless of the dose calculation algorithms and x‐ray energy. DSF can be considered one of the references for the density scaling factor of Delta4 phantom materials and may help improve the accuracy of the IMRT dose verification using Delta4.
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Affiliation(s)
- Kensuke Tani
- Department of Radiological Sciences, Graduate School of Tokyo Metropolitan University, Arakawa, Japan
| | - Yukio Fujita
- Department of Radiation Oncology, Tokai University School of Medicine, Isehara, Japan
| | - Akihisa Wakita
- Department of Radiation Oncology, National Cancer Center Hospital, Tsukiji, Japan
| | - Ryohei Miyasaka
- Department of Radiation Oncology, Chiba Cancer Center, Chiba, Japan
| | - Ryuzo Uehara
- Department of Radiation Oncology, National Cancer Center Hospital East, Kashiwa, Japan
| | - Takumi Kodama
- Department of Radiation Oncology, Saitama Cancer Center, Ina, Japan
| | - Yuya Suzuki
- Department of Radiation Oncology, Tokyo Dental College Ichikawa General Hospital, Ichikawa, Japan
| | - Ako Aikawa
- Department of Radiation Oncology, National Cancer Center Hospital, Tsukiji, Japan
| | - Norifumi Mizuno
- Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan
| | - Jiro Kawamori
- Department of Radiation Oncology, St. Luke's International Hospital, Tokyo, Japan
| | - Hidetoshi Saitoh
- Department of Radiological Sciences, Graduate School of Tokyo Metropolitan University, Arakawa, Japan
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Ballangrud Å, Kuo LC, Happersett L, Lim SB, Beal K, Yamada Y, Hunt M, Mechalakos J. Institutional experience with SRS VMAT planning for multiple cranial metastases. J Appl Clin Med Phys 2018; 19:176-183. [PMID: 29476588 PMCID: PMC5849827 DOI: 10.1002/acm2.12284] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Revised: 12/15/2017] [Accepted: 12/27/2017] [Indexed: 12/14/2022] Open
Abstract
Background and Purpose This study summarizes the cranial stereotactic radiosurgery (SRS) volumetric modulated arc therapy (VMAT) procedure at our institution. Materials and Methods Volumetric modulated arc therapy plans were generated for 40 patients with 188 lesions (range 2–8, median 5) in Eclipse and treated on a TrueBeam STx. Limitations of the custom beam model outside the central 2.5 mm leaves necessitated more than one isocenter pending the spatial distribution of lesions. Two to nine arcs were used per isocenter. Conformity index (CI), gradient index (GI) and target dose heterogeneity index (HI) were determined for each lesion. Dose to critical structures and treatment times are reported. Results Lesion size ranged 0.05–17.74 cm3 (median 0.77 cm3), and total tumor volume per case ranged 1.09–26.95 cm3 (median 7.11 cm3). For each lesion, HI ranged 1.2–1.5 (median 1.3), CI ranged 1.0–2.9 (median 1.2), and GI ranged 2.5–8.4 (median 4.4). By correlating GI to PTV volume a predicted GI = 4/PTV0.2 was determined and implemented in a script in Eclipse and used for plan evaluation. Brain volume receiving 7 Gy (V7 Gy) ranged 10–136 cm3 (median 42 cm3). Total treatment time ranged 24–138 min (median 61 min). Conclusions Volumetric modulated arc therapy provide plans with steep dose gradients around the targets and low dose to critical structures, and VMAT treatment is delivered in a shorter time than conventional methods using one isocenter per lesion. To further improve VMAT planning for multiple cranial metastases, better tools to shorten planning time are needed. The most significant improvement would come from better dose modeling in Eclipse, possibly by allowing for customizing the dynamic leaf gap (DLG) for a special SRS model and not limit to one DLG per energy per treatment machine and thereby remove the limitation on the Y‐jaw and allow planning with a single isocenter.
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Affiliation(s)
- Åse Ballangrud
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Li Cheng Kuo
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Laura Happersett
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Seng Boh Lim
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Kathryn Beal
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Yoshiya Yamada
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Margie Hunt
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - James Mechalakos
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA
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