PSOR8  Presentation Time: 12:05 PM: ABCD: An HDR Prostate Brachytherapy Optimizer with Mixed Bound / Unbound Functionalities.

To develop ABCD, an HDR brachytherapy prostate optimizer with mixed bound and unbound functionalities and evaluate its performance. ABCD utilized linear optimization with iterative constraint refinement. ABCD aims to maximize (unbounded) dose to voxels within the prostate while achieving bounded constraints on organs-at-risk (urethra and rectum D max). 20 HDR prostate plans were retrospectively optimized using ABCD and with a commercial optimizer (VEGO, Varian Medical Systems) with constraints of rectum D max < 17.1Gy and urethra D max < 22.8Gy. These constraints were chosen to mimic potential dose constraints for monotherapy prostate HDR patients. For VEGO, a prostate D 90 objective iteratively increased by the user until rectum and urethra limits were reached was used. Prostate V 19Gy , D 90 , D 98 and D min were reported. Statistical comparison was performed using a paired T-test (p < 0.05 for significance). ABCD vs VEGO prostate metrics were (median with range): V 19Gy = 98.3 (85.8 - 100) % vs 95.9 (87.5 - 99.6, p = 0.008 < 0.05) %; D 90 = 20.8 (18.3 - 22.3) Gy vs 21.0 (18.2 - 23.2, p = 0.1 > 0.05) Gy; D 98 = 19.1 (16.6 - 21.1) Gy vs 17.7 (14.1 - 20.0, p = 8 × 10−5 < 0.05) Gy; D min = 16.5 (15.2 - 18.7) Gy vs 12.5 (10.5 - 16.4, p = 4 × 10−10 < 0.05) Gy. ABCD respected rectum and urethral constraints; commercial optimizer plans had to be rescaled to meet the constraints. Dose escalation to the prostate was possible with ABCD without iterative optimization by the user. While ABCD did not specifically aim to escalate D 90 dose, it achieved similar results compared to specific D 90 escalation strategies with a commercial optimizer while at the same time permitting statistically significant dose escalation of all other metrics investigated. Further work is ongoing to investigate the utility in DIL boosts, as well as integrating needle suggestions within the optimization step to provide superior dose coverage. [ABSTRACT FROM AUTHOR]