Pelvic SABR with HDR boost in intermediate- and high-risk prostate cancer (SPARE): Favorable early toxicity and quality-of-life outcomes.

Abstract

60 Background: ASCENDE-RT has provided level 1 evidence supporting the use of androgen deprivation therapy (ADT), external beam radiotherapy and brachytherapy boost in intermediate- and high-risk prostate cancer. The objectives of this study are to report early toxicity and quality of life (QOL) outcomes in patients treated on a hybrid protocol using five-fraction pelvic stereotactic ablative radiotherapy (SABR) with a MRI dose painted HDR brachytherapy boost (HDR-BT). Methods: A phase I/II study was performed where intermediate (IR) and high-risk (HR) prostate cancer patients received HDR-BT 15Gy in single fraction to the prostate and up to 22.5Gy to the MRI nodule. Gantry-based 25Gy SABR was delivered to pelvis, seminal vesicles and prostate in 5 weekly fractions. ADT was used for 6-18 months. Common Terminology Criteria for Adverse Events version 3.0 was used to assess toxicities. QOL was captured using EPIC at every follow-up. A minimally clinically important change (MCIC) definition was triggered if the EPIC QOL score at each time point decreases > 0.5 SD, where SD is the standard deviation of baseline scores. Results: Thirty-three patients (NCCN 6.0% low IR, 45.5% high IR and 48.5% HR) completed this treatment with a median follow-up of 13.8 months (IQR 12.1, 18.8). The incidence of worst toxicities is shown in Table 1.The 3 grade 3 GU patients were due to temporary urinary catheterization in the acute period following HDR-BT. Mean (95% SD) EPIC urinary QOL scores were 82.5 (16.5), 83.2 (12.9) and 83.7 (16.3) at baseline, 3 months and 12 months and the bowel scores were 95.9 (3.8), 92.6 (8.2) and 90.5 (8.3), respectively. Proportion of patients experiencing MCIC at 3 months and 12 months were 20.8% and 14.3% for urinary domain, 47.8% and 53.9% for bowel domain; respectively (see Table). Conclusions: This novel treatment protocol incorporating MRI dose painted HDR brachytherapy boost and SABR pelvic radiation for intermediate- and high-risk prostate cancer in combination with ADT is feasible and well tolerated in the acute setting. Clinical trial information: REB 269-2014. [Table: see text]