M Trager, J Beaudry, D Aramburu Nunez, G Cohen, L Dauer, D Gorovets, N Hassan Rezaeian, M Kollmeier, B Leong, P McCann, M Williamson, M Zelefsky, A Damato*, Memorial Sloan Kettering Cancer Center, New York, NY

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  A Damato

PO-GePV-T-4 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To quantitatively evaluate clinical significance of potential HDR prostate brachytherapy (HDRPB) physics errors through automated simulations.

Methods: Three idealized HDRPB geometries with rectum, urethra and different sized prostate contours were generated in BrachyVision. High and low dwell-time modulated plans using clinical constraints were created per geometry. Based on FMEA analysis, four high-impact errors applicable to HDRPB were selected for quantitative analysis. Plans were exported, and error simulations and dose calculations were performed using MATLAB and Python routines: single (N=1,722) and systematic (N=126) catheter shifts (craniocaudal; -1cm:1cm); single catheter digitization errors (tip and connector needle-tips displaced independently in random directions; 0.1cm:0.5cm; N=44,318); and swaps (two catheters swapped during digitization or connection; N=528). The deviations due to each error on Prostate_D_90%, Urethra_D_20% and Rectum_D_1cc were analyzed using two thresholds considered for clinical significance: 5-20% (possible clinical impact [PCI]) and >20% (likely clinical impact [LCI]).

Results: Single catheter shifts resulted in a PCI for <6% of simulations for small geometry with large shifts (≥0.8cm), and no LCI. Systematic catheter shifts had the largest clinical impact on Prostate_D_90% with 100% of simulations resulting in a PCI for shifts ≥0.5cm and LCI for shifts ≥0.8cm. Systematic shifts had no clinical impact on Urethra_D_20%; for Rectum_D_1cc PCI occurred in 25% of shifts ≥0.5cm with no LCI. Digitization errors resulted in PCI for all structures but LCIs only for Urethra_D_20cc. As prostate size and modulation decreased, impact on prostate and rectum increased while urethra decreased. Swaps had PCI 14%, 21% and 9% of the time for Prostate_D_90%, Urethra_D_20% and Rectum_D_1cc, respectively.

Conclusion: Prostate_D_90% and Rectum_D_1cc had the highest chance of PCI from systematic catheter shifts, while Urethra_D_20% was from swaps. LCI was uncommon for all combinations, besides systematic catheter shift’s impact on Prostate_D_90%. Digitization errors most consistently caused PCI for all scenarios.

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Keywords

Brachytherapy, HDR, Prostate Therapy

Taxonomy

TH- Brachytherapy: prostate brachytherapy

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