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Program Information

Application of the AAPM TPS Professional Practice Guideline in Commissioning a Paired Prototype Linear Accelerator/TPS

Y Li

Y Li1,2*, T Netherton1 , P Nitsch1 , A Klopp1 , L Court1 , P Balter1 , S Gao1 , (1) The University of Texas MD Anderson Cancer Center, Houston, TX, (2) The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX


TH-CD-205-12 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 205

Purpose: To commission and evaluate the AAA(Varian) standard 6MV-FFF beam model for a prototype linac with a novel jawless dual-level, high-speed MLC collimation system, and capabilities of faster IMRT and VMAT treatments.

Methods: We followed all tests recommended by MPPG5a. The dose distributions calculated by the TPS in water were compared with measured PDD and off-axis factors(OAF) for various field sizes (2x2-28x28 cm2). In addition, asymmetric fields, a mantle field, a half-beam block field, and an obliquely incident field were used for profile and point-dose comparisons. To validate heterogeneity corrections, an anthropomorphic thorax phantom(CIRS) was used to measure normal tissue dose in treatment mode which was then compared to TPS calculation. Patient specific QA was performed for 9 IMRT and 9 VMAT plans using ArcCheck(SunNuclear). End -to-end tests were conducted using IROC head-and-neck and lung phantoms.

Results: PDD and OAR measurements were in agreement with TPS calculations with average ratio of 0.991±0.014 and 1.007±0.047, respectively. The average point-dose differences between TPS calculation and measurement were 1.50±0.65% and 0.65±0.52% for plans with open field and irregular-surface compensator, respectively. The average profile difference was 2.88±1.58% for open fields. The dose in heterogeneous regions in the CIRS phantom was accurately modeled by the TPS with a 1.07±1.71% difference from the measurements. A VMAT plan was created for IROC head and neck phantom and an IMRT plan was created for IROC lung phantom. The gamma passing rates(3mm/3%) for QA of 9 IMRT and 9 VMAT plans were 98.4% and 99.5%. Both end-to-end tests passed with an average dose ratio (measurement/TPS) of 0.99 and 0.97, and an average gamma passing rate (7%/4mm) for film profiles of 99% and 98.8% for head-and-neck phantom lung phantom, respectively.

Conclusion: This prototype LINAC shows promising potential in clinical use, especially for faster IMRT and VMAT treatments.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Varian Medical Systems.

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