C Frank*, P Ramesh, Q Lyu, D Ruan, S Park, K Sheng, Department of Radiation Oncology, University of California Los Angeles, Los Angeles

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  C Frank

SU-K-207-2 (Sunday, 7/10/2022) 5:00 PM - 6:00 PM [Eastern Time (GMT-4)]

Room 207

Purpose: To develop an efficient deterministic inverse planning framework for HDR prostate brachytherapy treatment planning with automated catheter location selection and simultaneous dual-energy source dwell time optimization.

Methods: The optimization was performed using the fast-iterative shrinkage-thresholding algorithm (FISTA) and a group sparsity term to select the same number of catheters as used in the clinical Ir-192 plans, ranging from 16-21, from a set of >60 candidate channels. The plans were generated using 10 Ci Varian Varisource (VS2000 192Ir) and 10 Ci Model M42 169Yb HDR sources, modeled according to the TG-43U1 formalism. Single and dual-source treatment plans were generated using our optimization engine for 18 patients. The single and dual-source deterministic treatment plans and the clinical plan using stochastic optimization for each patient were normalized to deliver a 15 Gy/fx dose to 95% of the prostate (CTV). The doses to the maximally irradiated 0.1 cc of the urethra, bladder, and rectum (D0.1cc) were calculated and compared.

Results: The mean differences in bladder and rectum D0.1ccs between the dual source plan and the Ir-only plans were not significantly different. Further, the difference in the bladder D0.1cc among the dual-source, the Yb-only, and clinical plans was not significant, while the differences in the rectum D0.1cc between the dual-source and Yb-only plan (-4.78% of CTV Rx dose, p = 0.0014) and between dual-source and clinical plans (5.76%, p = 0.0035) were statistically significant. The average differences in the urethral D0.1cc from the clinical, Yb-only, and Ir-only plans compared with dual-source plans were -3.33% (p = 2.57*10-4), -8.33% (p = 1.60*10-7), and -1.98% (p = 2.65*10-4) of the prescription dose, respectively.

Conclusion: Our deterministic inverse brachytherapy treatment optimization engine can successfully optimize catheter locations and produce multi-energy treatment plans. Further, the dual-source plans show increased urethral sparing over the clinical and optimized single-source plans.

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