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Comparative Efficacy of Image-Guided Adaptive Treatment Strategies for Prostate Radiation Therapy Via Virtual Clinical Trials

M Sharma

M Sharma*, J Williamson, J Siebers, Virginia Commonwealth University, Richmond, VA

MO-A-137-2 Monday 8:00AM - 9:55AM Room: 137

Purpose: To determine potential dosimetric benefits of image guided adaptive radiation therapy treatment (IGART) strategies for intermediate risk prostate cancer via automated virtual clinical trials (VCTs).
Materials and Methods: A 19 patient cohort with 8-13 CT images was used to compare different IGART strategies. The IMRT prescription was 46 Gy/23 fractions to the prostate and seminal-vesicle PTVs, followed by a 40 Gy/20 fractions prostate boost. For each patient, daily IGART imaging was simulated by random selection from available images. The VCTs simulated three different IGART-IMRT strategies; (A0) initial planning only with 5 mm PTV margins; (A1) daily re-planning without considering prior dose; and (A2) online daily re-planning for each fraction considering prior dose obtained via deformable dose mapping (A1 and A2, no PTV margin). For each strategy, daily dose was deformably mapped using Demons-based displacement vector fields and accumulated to estimate the treatment dose. Strategies were compared via dosimetric adherence to constraints (CTV D98=86.4, D2<94.6Gy), and objectives (CTV D98<86.4, D2<91.2Gy; bladder D2<90, D20<70, D30<56, D50<39, EUD=0 Gy; and rectum D2<83, D20<70, D30<56, D50<39, EUD=0 Gy).
Results: A0 had larger doses to 20, 30, and 50% rectal (30±20%) and bladder (40±20%) volumes than A1 and A2 (p<0.001). Rectal and bladder D2s were also respectively higher in A0 by (15±13%) and (24±14%) (p=0.002 and 0.00001 respectively). Comparing A1 and A2, no significant differences were found in prostate D98 (p=0.4) or bladder D2 (p=0.33). Significant differences were found for the rectum (D5,A2>D5A1, p=0.02) .
Conclusions: IGART utilizing daily re-planning (A1 and A2) has dosimetric advantages over conventional IMRT for critical structures, particularly high-dose regions, without compromising PTV coverage. Due to inherent deformation vector field inaccuracies, daily re-planning based on prior dose (A2) showed poor rectal sparing than A1.

Funding Support, Disclosures, and Conflict of Interest: NIH grant P01 CA 116602 and Philips Medical Systems

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