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Session: Therapy: Brachytherapy Treatment and QA [Return to Session]

Dual-Source Optimization for HDR Prostate Brachytherapy

H Frank*, S Park, K Sheng, UCLA School of Medicine, Los Angeles, CA


SU-IePD-TRACK 5-6 (Sunday, 7/25/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

Purpose: High dose rate (HDR) brachytherapy is used to treat prostate cancer in mono-, combination-, or salvage settings. Iridium-192 is the most common source, but Ytterbium-169 has also been considered for its lower energy and potential to spare nearby sensitive organs, e.g., the urethra. However, a planning method to optimize the utilization of both energy sources for efficient plan delivery has not been presented. In this study, we develop a framework that jointly optimizes Ir-192 and Yb-169 dwell times for urethra sparing with a total treatment time penalty.

Methods: The planning problem was formulated as a group sparsity optimization problem to minimize the number of channels used by both sources. The optimization problem was solved using the fast-iterative shrinkage-thresholding algorithm. The HDR source dose distributions were modeled following the AAPM TG-43 formalism for 10 Ci Varian Varisource (VS2000 ¹⁹²Ir) and 10 Ci Model M42 ¹⁶⁹Yb HDR sources. Three treatment plans were generated to deliver a 15 Gy/fx prescription dose for a retrospective patient with 19 channels using Ir-192 only, Yb-169 only, and dual-source.

Results: The three plans resulted in similar dose distribution to the PTV, rectum, and bladder. The minimum dose in the most irradiated 0.1 cm3 of the urethra were 15.13, 16.50, and 15.00 Gy for the Ir-192, Yb-169, and dual-source plans, respectively. The group sparsity term effectively reduced the total number of channels used for the dual-energy approach. The total dwell times were 15.41, 49.43, and 26.70 minutes for the Ir-192, Yb-169, and dual-source plans, respectively.

Conclusion: Dual-energy brachytherapy combines the penetration of high energy and rapid drop-off of low energy Gamma rays for greater flexibility in plan dosimetry. We developed a novel framework to optimize the delivery efficiency for dual-source treatment. Further improvement in plan dosimetry and OAR sparing may require optimization of catheter locations.



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