Toxicity and Patient Reported Quality of Life Outcomes Following Prostate SBRT with Focal Boost to MRI Identified Prostate Cancer Lesions: Results of a Phase II Trial

Abstract

<h3>Purpose/Objective(s)</h3> A focused boost to MRI identified prostate cancer lesions treated with radiotherapy has been shown to improve biochemical disease control without increased toxicity in standard fractionated radiation treatment. Prostate cancer is known to be sensitive to higher radiation doses per fraction and thus stereotactic body radiotherapy (SBRT) has become an increasingly popular treatment method. In this prospective phase II trial, we investigated the toxicity and patient reported quality of life outcomes in patients treated with SBRT to the prostate gland and a simultaneous focal boost to MRI identified intraprostatic lesions while also de-escalating dose to the adjacent organs at risk. <h3>Materials/Methods</h3> Eligible patients included low- or intermediate- risk prostate cancer (Gleason score ≤ 7, PSA ≤20, T stage ≤2b). SBRT was prescribed to 40 Gy in 5 fractions delivered every other day to the prostate, with areas of high disease burden (MRI-identified PI-RADS 4 or 5 lesions) escalated to 42.5-45 Gy and areas overlapping organs at risk (within 2 mm of urethra, anterior rectal wall, and bladder base) constrained to 36.25 Gy (n=98). Patients without a pre-treatment MRI were treated to dose of 37.5 Gy with no focal boost (n=14). Acute and late toxicity were graded using RTOG modified toxicity scales. Patient-reported outcome and quality of life was assessed using the AUA-IPSS lower urinary tract symptom score, IIEF-5 erectile function, and EPIC-26 surveys. Statistical testing was performed in statistical software. <h3>Results</h3> From 2015 to 2022, a total of 112 patients were enrolled with a median follow-up of 36 months. No acute or late grade 3+ GI or GU toxicity was observed. Within the focal boost arm, acute grade 2 GU toxicity during treatment or at 6-week follow-up was seen in 26% of patients. Acute grade 2 GI toxicity was seen in 1 patient. Cumulative late grade 2 GU toxicity was 8%. Rate of alpha blocker medication use following treatment was 26%. Cumulative late grade 2 GI toxicity was 2.3%. Patient reported outcomes showed no significant changes from baseline IPSS lower urinary tract, IIEF erectile function, or EPIC-26 urinary incontinence, urinary irritative, gastrointestinal, or sexual domain quality of life scores following treatment (p >0.05 for all tests via RANOVA). Two patients have had a biochemical recurrence to date, at 42 months and 60 months post treatment. <h3>Conclusion</h3> SBRT to a dose of 40 Gy to the prostate gland with a focal boost up to 45 Gy is well tolerated with no observed grade 3 toxicity and similar rates of acute and late grade 2 GI and GU toxicity as seen in other SBRT regimens without intraprostatic dose boost. Moreover, no significant changes were seen in patient reported urinary, bowel, or sexual outcomes from pre-treatment baseline at any follow-up date. Biochemical control data continue to mature but few treatment failures have been observed to date.