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Dosimetric Differences of Post HDR Prostate IMRT Plans Generated From RayStation Multi-Criteria Optimization (MCO) and Pinnacle Direct Machine Parameter Optimization (DMPO)

Y Chen*, X Liao, K Doxsee, C Yang, Monmouth Medical Center, Long Branch, NJ

SU-E-T-719 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate dosimetric differences of post HDR prostate IMRT plans generated from RayStation Multi-Criteria Optimization (MCO) and Pinnacle³ Direct Machine Parameter Optimization (DMPO)

Methods: Ten patients previously treated with DMPO plans on Pinnacle³ v9.0 were selected. CT images with same RT structures from Pinnacle were sent to RayStation v2.4.8.180 for re-planning using MCO Pareto surface plans with the same prescription and beam angles. The prescription was 50.4 Gy to 95% of PTV for all cases. Planning outcomes such as D₉₅ (95% of volume receiving the prescribed dose), D₅, D₂, D₁ for PTV, D₅₃ for bladder, D₅₃, D₃₀, and D1cc for rectum, D1cc for small and large bowel, conformity index (CI = PIV / PTV), and homogeneity index (HI = D₅ / D₉₅) were evaluated according to the clinical protocol.

Results: The mean volume of PTV was 222.6 cm3 (range from 178.5 to 276.3 cm3). The D₉₅ of PTV coverage of RayStation vs. Pinnacle was improved and more uniform with 49.8 Gy vs. 49.7 Gy, respectively. D₅, D₂, and D₁ of PTV were lower with RayStation. So were D₅₃ for bladder and rectum, D₃₀ for rectum (p = 0.017), D1cc for rectum and D1cc for small bowel, D1cc for large bowel except one case on RayStation. CI was better with RayStation compared to Pinnacle (1.01 vs. 1.07). HI was better with RayStation compared to Pinnacle (1.06 vs. 1.07).

Conclusion: MCO planning automatically generates a set of Pareto optimized solutions for given objectives to allow tradeoffs between targets and critical organs. RayStation can achieve better uniform tumor coverage with fewer hot spots while sparing more critical structures in post HDR prostate plans. MCO Pareto based plan is helpful in determining the best optimized dosimetry solutions.

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