SU‐E‐T‐284: Dose Plan Optimization When Using Hydrogel Prostate‐Rectum Spacer: A Single Institution Experience

Purpose: To describe rectal dose reduction achieved and techniques used to take advantage of the increased peri‐rectal spacing provided by injected polyethylene‐glycol. Methods: Thirty prostate cancer patents were 2:1 randomized during a clinical trial to evaluate the effectiveness of injected poly‐ethylene glycol hydrogel (SpaceOAR System) in creating space between the prostate and the anterior rectal wall. All patients received a baseline CT/MR scan and baseline IMRT treatment plan. Patients were randomized to receive hydrogel injection (n=20) or Control (n=10), followed by another CT/MR scan and treatment plan (single arc VMAT, 6 MV photons, 79.2 Gy, 44 fractions). Additional optimization structures were employed to constrain the dose to the rectum; specifically an avoidance structure to limit V75