Room: Exhibit Hall | Forum 4
Purpose: An ongoing multi-center randomized trial (POTEN-C) is evaluating the impact of neurovascular elements sparing SAbR on patient-reported sexual QOL for localized prostate cancer. MR-guided dose de-escalation is performed sparing one neurovascular bundle (NVB) in the experimental arm. In this work, we examine the practicality of focal HDR brachytherapy to salvage failures in the spared prostate without exceeding organ at risk (OAR) constraints.
Methods: Three patients with MR, CT, and transrectal ultrasound image sets having previously been treated with combined HDR/EBRT were used for this work. Acceptable plans for each patient were generated to satisfy constraints from the POTEN-C trial with PTV30(30Gy/5fx)=prostate+3mm and PTV45(45Gy/5fx)=PTV30-5mm of NVB. Four different focal failures in the spared area of prostate receiving â‰¤ 30Gy for each patient were modeled for salvage (apical, mid, base, and diffuse). A 5mm expansion from simulated failure GTV was used for the salvage PTV and planned to receive 27Gy/2Fx using the Eclipse Brachyvision planning system (Varian Medical System) using needles already present from the TRUS images. OAR constraints were based on existing HDR salvage protocols for conventional treatments, including urethra D100% < 110% and rectal V80% < 0.2mL.
Results: Plans with unilaterally spared NEs successfully met OAR constraints while achieving full coverage for simulated failures (average D100%=26.82Gy). Urethral doses were highest in diffuse and focal base failures (average Dmax=26.2Gy compare to Dmax=25.2Gy) but were within pre-specified constraints.
Conclusion: The feasibility of HDR salvage brachytherapy after neurovascular-sparing SAbR is demonstrated without compromising target coverage or OAR constraints. While salvage after SAbR is not well established, this protocol provides a realistic model for salvage HDR in the setting of anatomy-driven prostate cancer radiotherapy.