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Correlating Dose-Volume Histogram Results with Overlapping Volume of Organ-At-Risk and Planning Target Volume for Prostate IMRT

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T Ma

T Ma*1, IZ Wang1,2 , (1) The State University of New York at Buffalo (2) Roswell Park Cancer Institute, Buffalo, NY


SU-E-T-530 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Meeting the dose constrains of organs-at-risk (OAR) in an inversely planned IMRT case may not be sufficient for judging it as an optimal treatment plan. The purpose of this study is to investigate whether the percentage of overlapping volume (POV) between the OAR and planning target volume (PTV) over the original organ volume can be used as an additional indicator for evaluating the quality of an IMRT treatment plan.
Methods: In the study, we selected 31 prostate cancer patients, previously treated with IMRT utilizing volumetric modulated arc therapy (VMAT) technique. The overlapping volumes were contoured based on the initial treatment plans using boolean operation in Eclipse treatment planning system (Varian Medical System). For each patient, a prescription dose of 79.2 Gy (1.8 Gy /fraction) was given to the PTV, which has a 10 mm margin (6 mm posterior) outside the prostate. All 31 clinical prostate treatments were planned to deliver at least 95% prescribed dose to the PTV. The dose-volume histograms (DVHs) of bladder and rectum were calculated and analyzed. The POV between bladder and PTV (POVb) and the POV between rectum and PTV (POVr) were acquired and the correlation between POVs and the selected dose-volume parameters were then analyzed for each OAR.
Results: The correlation between POVb and D15%, D25%, D35% and D50% for bladder was found to be very good in general (R²=0.71-0.79 in a linear fit). Whereas for rectum the correlation between POVr and D15%, D25%, D35% and D50% was highly correlated at D15%, then showed a trend to become weaker towards D50% (R²=0.10-0.65 in a linear fit).
Conclusion: A correlation exists between DVH parameters and POV of OAR in the optimized clinical prostate plans. Hence, DVH results versus POV can be used as an additional reference for evaluating a prostate cancer IMRT treatment plan.

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