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A Plan Quality Index in IMRT QA That Is Independent of the Acceptance Criteria
D Kim1*, S Kim2 , S Kang1 , T Kim1 , K Kim1 , S Park1,3 , M Cho1 , D Shin1 , T Suh1 , (1) The Catholic University of Korea, Seoul, Korea, Republic of, (2) Virginia Commonwealth University, Richmond, VA, (3) Uijeongbu St.Mary's Hospital, GyeongGi-Do, Korea, Republic of
Presentations
SU-E-T-60 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: In IMRT QA, plan quality evaluation is made based on pass rate under preset acceptance criteria, mostly using gamma-values. This method is convenient but, its result highly depends on what the acceptance criteria are and suffers from the lack of sensitivity in judging how good the plan is. In this study, we introduced a simple but effective plan quality index of IMRT QA based on dose difference only to supplement such shortcomings, and investigated its validity.
Methods: The proposed index is a single value which is calculated mainly based on point-by-point comparison between planned and measured dose distributions, and it becomes “1” in an ideal case. A systematic evaluation was performed with one-dimensional test dose distributions. For 3 hypothetical dose profiles, various displacements (in both dose and space) were introduced, the proposed index was calculated for each case, and the behavior of obtained indices was analyzed and compared with that of gamma evaluation. In addition, the feasibility of the index was assessed with clinical IMRT/VMAT/SBRT QA cases for different sites (prostate, head & neck, liver, lung, spine, and abdomen).
Results: The proposed index showed more robust correlation with the amount of induced displacement compared to the gamma evaluation method. No matter what the acceptance criteria are (e.g., whether 3%/3mm or 2%/2mm), it was possible to clearly rank every case with the proposed index while it was difficult to do with the gamma evaluation method.
Conclusion: IMRT plan quality can be evaluated quantitatively by the proposed index. It is considered that the proposed index would provide useful information for better judging the level of goodness of each plan and its result is independent of the acceptance criteria.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid-career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
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