A Pilot Study of Salvage HDR Brachytherapy in Recurrent Prostate Cancer: 5 Year Toxicity and Outcomes

Abstract

<h3>Purpose/Objective(s)</h3> Until recently, Androgen Deprivation Therapy (ADT) was the main treatment option for recurrent prostate cancer after primary radiation treatment. However, ADT is not curative and is associated with several side effects. Local ablative therapy can be curative and reduce long-term side effects associated with ADT. We designed a single institution prospective pilot study to evaluate the toxicities and outcomes of HDR brachytherapy as a salvage local therapy. <h3>Materials/Methods</h3> Sixty (60) patients with a biopsy-proven local relapse after a previous treatment with radiation were included in this study. A negative bone scan and CT scan of the abdomen and pelvis at the time of relapse was mandatory. Primary objective was to assess both early and late genitourinary (GU) and gastrointestinal (GI) toxicities. Biochemical disease-free survival (bDFS) was also assessed as a secondary objective. Toxicities were reported using CTCAE v5 scale and the IPSS. Short-course ADT could be used if deemed clinically indicated by the physician. HDR brachytherapy regimen was 32Gy delivered in 4 fractions to the whole prostate and, for the last 10 patients recruited, 27Gy in 2 fractions administered focally, due to concerns with toxicities. CT-based treatment planning using an inverse planning algorithm (IPSA) was performed for patients with whole prostate treatment (n = 50). Real-time ultrasound-based treatment planning was used for patients undergoing focal salvage radiation (n = 10). <h3>Results</h3> Median follow-up was 58.4 months (0.8-106.8 months). GI toxicities were acceptable with 3.6% and 14.5% of patients experiencing early and late grade 2 toxicities. No G3 GI toxicities were reported. Early G2 GU toxicities were overestimated at 100% (all patients used an alpha-blocker in the postoperative setting) and one patient had G3 early toxicity. Late GU toxicities were significant, with 14.5% of patients experiencing late G3 toxicity (10.0% at the last follow-up). Of interest, the use of ADT before HDR brachytherapy (n = 17) was associated with lower GU toxicities (no G3) although the association was not statistically significant (Chi-Square p-value 0.201). Good biochemical control was achieved with a bDFS of 73.9% at 48 months. <h3>Conclusion</h3> Salvage HDR brachytherapy after primary radiation to the prostate offers good biochemical control but at the cost of significant G3 GU morbidities. Patients can benefit from local therapy after primary radiation but whole-gland radiation should be used with caution because of concern with toxicities. Focal therapy to partial gland might be a good alternative to achieve local control and avoid severe toxicities.