SU‐C‐110‐01: Strategies for Online Plan Re‐Optimization: Objective Settings and Starting Stage
Purpose: To find the most robust strategies of objective setting and starting stage for online plan re‐optimization, so it can be automatically executed within 1 min while providing high quality adaptive plans. Methods: 10 prostate cancer patients, each with 1 planning‐CT and 5 CBCTs, were retrospectively studied to simulate daily re‐optimization. PTV objectives were (same across plans): D95>100% and Dmax<110%. Three OAR optimization objectives were compared: RTOG objectives (same across patients); DVH parameters extracted from original CT‐plans (CT objectives); and DVH parameters extracted from “goal” dose distributions obtained through deformable registration between planning‐CT and CBCT (Deformed‐CT objectives). Two starting stages were compared: optimal‐fluence in original CT‐plan (Warm‐start) and unity‐intensity within PTV (Cold‐start). Conformity index (CI) and homogeneity index (HI) were calculated to assess the target coverage. OAR sparing was evaluated by V50%/V100% for the bladder and V50%/V70Gy for the rectum. Delivery efficiency was evaluated by total‐MU of each plan. Results: (1)Target: CIs (all<1.2) were similar for all objective settings with either Warm‐ or Cold‐start. However, HIs were consistently lower for RTOG (p<0.0001). (2)Rectum: Deformed‐CT objectives achieved slightly lower V70Gy (<2.5cc) than CT or RTOG (p<0.0001). Both CT and Deformed‐CT objectives achieved lower V50% (p<0.0001) than RTOG by 5.7%–23.6%. (3)Bladder: Deformed‐CT and CT objectives had small differences in V100%/V50%, but were better than RTOG (p<0.0001), especially for V50% (6.8%–16.9% reduction). (4)Warm‐start increased total‐MU by 23%±11% for all plans, but also reduced V50% by 9.7%–26.9% for rectum with all objective settings, and reduced V50% by ∼10% for bladder with RTOG setting. (5)Deformed‐CT objectives showed greater advantage over CT objectives when OAR volume in CBCT is >30% larger than planning‐CT. Conclusions: CT and Deformed‐CT objectives are in general superior to RTOG for OAR sparing. Deformed‐CT objective is more robust when OAR volume significantly increases. Warm‐start has better OAR sparing, but significantly increases total‐MU. Research partially supported by a master research grant from Varian Medical Systems. © 2011, American Association of Physicists in Medicine. All rights reserved.
li, T; Zhang, Y; wu, Q; Yuan, L; Yin, F
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