Friday, June 17, 20229:00 AM - 10:00 AM PP01 Presentation Time: 9:00 AM: Propensity-Matched Analysis of High-Dose-Rate Brachytherapy in Intermediate Risk Prostate Cancer: Monotherapy or Boost?

Abstract

<h3>Purpose</h3> High-Dose-Rate Brachytherapy (HDR BT) either as monotherapy or boost has excellent reported prostate cancer control outcomes. Monotherapy is more commonly used for those with favorable risk features, while HDR tends to be combined with external beam radiotherapy (EBRT) for those with higher risk disease. Patients with intermediate risk prostate cancer (IR-PCa) can be managed either with monotherapy or boost. In the absence of randomized data, our objective is to compare biochemical response and oncological outcomes for patients with intermediate risk prostate cancer treated with either HDR as monotherapy or as a boost in combination with EBRT. <h3>Materials and Methods</h3> A propensity score matching analysis was performed of IR-PCa patients treated with either HDR monotherapy (27 Gy in 2 fractions), or HDR boost (15 Gy followed by EBRT; 37.5 Gy in 15 fractions delivered with Intensity modulated radiotherapy). The former patients were included in a prospective clinical trial whereas the latter were selected from a retrospective institutional database. Matching was based on age, baseline PSA, T stage, grade group, perineural invasion, and percentage of positive cores. No patient received androgen deprivation therapy. The primary outcome was biochemical disease-free survival (bDFS) defined as time from treatment to PSA nadir +2 or death. Secondary outcomes included PSA nadir and incidence of grade (G) ≥3 genitourinary (GU) and gastrointestinal (GI) toxicities measured using CTCAE v.4. A General Linear Mixed Model and Analysis of Covariance was used to investigate changes in PSA over time. <h3>Results</h3> A total of 132 patients were matched, 66 in each cohort with a median age of 66 years (range: 48-80). Median follow up was 59 months (interquartile range (IQR) 54, 62) for the HDR monotherapy cohort and 63 months (IQR 42, 81) for the boost BT group. They were well matched with a Propensity Score of 0.4615 and 0.4612, respectively. Thirty-eight percent of patients had unfavorable intermediate risk disease. Patients treated with monotherapy had slightly higher PSA in the first 4 years, Figure 1 (p=0.034), although by 5-years median PSA was 0.14 ng/ml (IQR 0.06, 0.34) with monotherapy and 0.15 ng/ml (IQR 0.07, 0.51) with boost. At 4 years, 24 (36%) monotherapy patients and 26 (44%) boost patients had PSA <0.2 ng/ml. Among all patients, 7% (10 of 132) experienced biochemical failure: six patients in the HDR monotherapy group and four in the boost group, resulting in 5-year bDFS of 93.5% and 93.3%, respectively. Favorable and Unfavorable IR-PCa had similar risk of recurrence. Late G3 GU toxicity occurred in 2 out of 66 boost patients and was not seen in the monotherapy patients. <h3>Conclusions</h3> Although limited by small sample size, we report high efficacy of HDR brachytherapy as either monotherapy or boost for all patients with intermediate risk disease. Boost patients had a lower PSA value in the first 4 years, although with a suggestion of greater G3 urinary toxicity.