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The Impact of Standardization of Gamma Criteria On Imaging Radiation Oncology Core Phantoms Analysis

F Brooks1*, M Glenn1, M Hussein2, C Clark3, J Lye4, J Lehmann5, I Silvestre2, S Kry1, (1) The University of Texas MD Anderson Cancer Center, Houston, TX, US, (2) National Physics Laboratory, Teddington, UK, (3) Royal Marsden Hospital, London, UK, (4) Australian Clinical Dosimetry Service, ARPANSA, Melbourne, AU, (5) Newcastle Mater Hospital, Newcastle, AU

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

PURPOSE: Establishing a global standard between clinical trial groups is a core goal of the Global Harmonization Group (GHG). This work seeks to evaluate the impact of different gamma criteria for two frameworks relevant to clinical trial QA.

METHODS: Twelve head and neck phantoms, each containing films in axial and sagittal orientations, were irradiated following clinical protocols. Gamma analysis was conducted on each film plane using CERR. The analysis was performed utilizing protocols from two different frameworks: Imaging Radiation Oncology Core (IROC) and GHG standards. The IROC method uses a normalization dose of 6.6 Gy and a 0% threshold, while the common ground method, proposed by GHG, requires plans to be normalized to the maximum dose in the measured dose distribution and a low dose threshold of 20%. Within each framework, the percent of pixels passing and mean gamma were evaluated at 7%/ 4mm, 5%/5mm, 3%/3mm, 3%/2mm, and 2%/2mm.

RESULTS: Based on the above criteria, the percent difference between the average percent of pixels passing for the IROC and GHG protocols ranged from 2-4%; the p-values were significant for all of the criteria except for 2%/2mm. The percent difference between the average mean gamma values for the IROC and GHG methods ranged from 1-6%; the p-values were significant for all criteria except for 3%/3mm and 2%/2mm. Differences in criteria and input parameters resulted in four pass/fail status changes for both 7%/4mm and 5%/5mm criteria.

CONCLUSION: An evaluation of the results provides quantification of the effects of gamma criteria and framework on the average percent of pixels passing gamma and the average gamma values. Careful attention should be given to acceptance criteria when comparing results between global clinical trial groups.

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Funding Support, Disclosures, and Conflict of Interest: This work is supported by Public Health Service Grants CA180803 and CA214526, awarded by the National Cancer Institute, United States Department of Health and Human Services.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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