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Impact of Phantom Rotation and Dose Gradient On 3D Gamma Evaluation

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K Kim

K Kim1*, D Kim1 , T Kim1 , S Kang2 , D Shin1 , M Cho3 , Y Noh4 , T Suh1 , (1) The Catholic University of Korea, Seoul(2) Seoul National University Hospital, Seoul, (3) Asan Medical Center, Songpa-gu,Seoul, (4) Eulji University Hospital, Daejeon


SU-I-GPD-T-290 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In intensity modulated radiation therapy (IMRT) quality assurance (QA) using dosimetric phantom, a spatial uncertainty induced from phantom set-up inevitably occurs and gamma index that is used to evaluate IMRT plan quality can be affected differently by a combination of the spatial uncertainty and magnitude of dose gradient. In this study, we investigated the impacts of dose gradient and the phantom set up error on 3D gamma evaluation.

Methods: Various dose distributions that have different dose gradients each other were designed to be used as calculation dose data in gamma evaluation, and several dose gradients that were used as measurement dose data were simulated by applying different rotation errors that had different rotation degrees, to each calculation dose data. 3D gamma evaluations were performed between all of the calculation and measurement dose distributions, and the results of gamma evaluations were sorted according to the magnitude of dose gradients and the rotation degrees.

Results: The 3D gamma pass rate showed insensitivity in relatively low dose gradients and no linear decrease with increase of rotation error. In general, low gamma pass rate showed at high dose gradients cases.

Conclusion: We conformed the behavior of 3D gamma evaluation with various dose gradient and rotation scheme, by inspecting gamma pass rate, maximum and minimum value. As a result, gamma showed insensitivity and false negative at the certain dose gradients and rotation error.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the Mid-career Researcher Program through NRF funded by the Ministry of Science, ICT & Future Planning of Korea (NRF-2014R1A2A1A10050270) and by the Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2015M2A2A7038291)

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