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Improving the Detectability of the Prostate During Hypofractionated Radiation Treatment Using EPID

T Ma

T Ma*, J Kilian-Meneghin , L Kumaraswamy , Roswell Park Cancer Institute, Buffalo, NY


TU-C3-GePD-J(A)-6 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: Hypofractionated prostate radiotherapy has the advantage of maximizing tumor kill while minimizing toxicities to rectum and bladder due to the relatively low α/β ratio for prostate compared to rectum and bladder. However, large prostate movements during treatment can reduce the therapeutic effectiveness of the hypofractionated treatments. Real-time monitoring can help accurately locate the target and, potentially, narrow the tumor margin to alleviate post-treatment radio-toxicities. The aim of this study is to maximize detectability of the prostate during hypofractionated VMAT treatments with real time EPID imaging.

Methods: Patients routinely will have at least three fiducial markers (FMs) implanted inside the prostate before computed tomography scan are acquired for treatment planning. During VMAT delivery, the detectability of the FMs is a challenge due to the dynamic MLC movement. In-house software was developed to extract the marker locations and project them onto the EPID detector. Detecting radius and FM separation distance can be set to estimate the probability of FM detection in real-time. The overall detectability score and overall percentage time of FM detection for at least two separate FMs were obtained to evaluate the probability of FM detection. Radiation treatment plans were re-optimized to take the FMs detectability into account.

Results: The Detectability score (SD) studied in the four original treated plans has an averaged value of 0.41±0.13. While the total percentage time of fiducial marker detection (TD) was 0.38±0.17. After optimization for FM detection, SD increased by 12% and TD had a significant improvement to 0.49±0.16, an increase of detection time by 28.9%.

Conclusion: The results indicated that incorporating the FM detectability into plan optimization greatly enhances the localization of the target in hypofractionated prostate treatments.

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