Safety and Early Efficacy of Involved Field SBRT for Nodal Oligo-Recurrent Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Following definitive treatment for localized prostate cancer a subset of men will unfortunately develop recurrent disease. Newer PET agents have demonstrated that most early recurrences occur in the abdominopelvic nodal basins. The optimal treatment strategy for this patient population is unknown but likely includes a combination of systemic therapy, surgery and/or radiation therapy. For radiation therapy, the optimal treatment volume, fractionation schedule and dose remain unanswered questions. We report early outcomes for patients treated with involved field SBRT for nodal oligo-recurrent prostate cancer. <h3>Materials/Methods</h3> Between January 2018 and January 2020, 21 patients with nodal oligo-recurrent prostate cancer treated with involved field SBRT at a single academic institution were eligible for inclusion in this analysis. Detection of recurrence was ascertained by imaging including: Axumin PET/CT (66%) or MRI/CT (34%) following a PSA rise. All patients were treated with five-fraction involved field SBRT to a dose of 27.5-30 Gy. The treatment volume for involved field was defined as the nodal basin containing the gross nodal disease as well as the immediately adjacent nodal basins. Oligo-recurrence was defined as any volume of disease that could be safely treated within an involved field. Acute and late toxicity data was defined as any treatment related toxicity occurring <b>≤</b> 90 days and > 90 days following treatment, respectively. Toxicity was graded using Common Terminology Criteria for Adverse Events version 4.0. PSA response was defined as any decrease in the PSA following treatment. Local recurrence was defined as any new or growing lesion within the treatment field following treatment. Local control was calculated using the Kaplan-Meier method. <h3>Results</h3> The median pre-salvage PSA was 7.2 ng/ml. The median follow-up for all patients was 25 months (11 – 36 months). The most common acute side effect was grade 1 diarrhea (n = 7, 33%). Acute grade 2 GI toxicity occurred in 14% of patients (n = 3). Two patients had late low grade pelvic pain and 1 patient had late grade 2 lower extremity limb edema. There were no late grade 2+ GI side effects. No grade 3+ side effects occurred at any time following treatment. 88% of patients had a PSA response following treatment. The local control at 1 and 2 years was 100% and 94%, respectively. <h3>Conclusion</h3> With the widespread adoption of novel PET agents the group of patients with oligo-recurrent nodal disease is likely to increase significantly. The optimal combination of local and systemic therapy in this patient population is the subject of ongoing clinical investigation. With a favorable toxicity profile, high rates of local control and PSA response, involved field SBRT represents a feasible as well as convenient local therapy treatment option for an elderly patient population.