Early Outcomes and Decision Regret Using PSMA/MRI-Guided Focal Boost for Prostate Cancer SBRT

Abstract

Purpose: Stereotactic body radiation therapy (SBRT) is a recognized treatment for low- and intermediate-risk prostate cancer, with 36.25 Gy in 5 fractions the most commonly used regimen. We explored the preliminary efficacy, patient recorded toxicity, and decision regret in intermediate- and high-risk prostate cancer receiving SBRT with prostate-specific membrane antigen (PSMA)/magnetic resonance imaging (MRI) guided focal gross tumor volume boost to 45 Gy.

Methods and materials: Between July 2015 and June 2019, 120 patients received SBRT across 2 institutions with a uniform protocol. All patients had fiducial markers and hydrogel, MRI and PSMA positron emission tomography (PET) scan. All patients received a questionnaire asking the degree of urinary, bowel, and sexual bother experienced at set time points, including questions about treatment choice and decision regret.

Results: One hundred twelve of 120 patients consented. Their median age was 72 years and median follow-up was 2.3 years. As per National Comprehensive Cancer Network guidelines, 78% had intermediate risk and 20% high risk. Androgen deprivation was combined with radiation in 6 patients. Most patients (74%) reported that receiving SBRT significantly influenced their choice of treatment. Five men (4%) expressed "quite a lot" (n = 4) or "very much" regret (n = 1) regarding their choice of treatment, while 89% expressed "no regret." Similar to pretreatment levels, "quite a lot" or "very much" urinary or bowel bother was expressed in 8% and 6% of patients, respectively. Two patients experienced nadir +2 biochemical failure, both found to have bone metastases. A third patient underwent PSMA PET at nadir +1.7 and had disease at the penile bulb, which was out of field. Three year estimated freedom from biochemical failure was 99% for intermediate and 85% for high-risk groups.

Conclusions: We have demonstrated promising efficacy and low toxicity with PSMA/MRI-guided SBRT focal boost. Less than 5% of patients expressed significant decision regret for their choice of treatment.