Early Tolerance and Tumor Control Outcomes with High-dose Ultrahypofractionated Radiation Therapy for Prostate Cancer

Abstract

BackgroundStudies using stereotactic body radiotherapy (SBRT) dose escalation in in low- and intermediate-risk prostate cancer patients have indicated favorable outcomes. ObjectiveTo evaluate tolerance and tumor control outcomes in low- and intermediate-risk prostate cancer patients treated with high-dose SBRT following our phase 1 trial. Design, setting, and participantsA total of 551 patients with low- or intermediate-risk prostate cancer were treated with SBRT. InterventionTreatment with 37.5–40Gy SBRT in five fractions directed to the prostate and seminal vesicles. Outcome measurements and statistical analysisOutcome measurements included acute toxicities (<3 mo after radiotherapy [RT]) and late toxicities (>3 mo after RT) and tumor control evaluation (prostate-specific antigen [PSA] levels at 3–6-mo intervals and post-treatment prostate biopsy at 2yr). Results and limitationsAcute grade 2 gastrointestinal (GI) toxicities occurred in 1.8% of patients, and late grade 2 and 3 GI toxicities were observed in 3.4% and 0.4% of patients, respectively. Acute grade 2 genitourinary (GU) toxicities occurred in 10% of patients, and grade 3 acute GU toxicities were observed in 0.7% of patients. Late grade 2 and 3 GU toxicities were observed in 21.1% and 2.5% of patients, respectively. The use of a hydrogel rectal spacer was significantly associated with reduced late GI toxicity and lower odds of developing late GU toxicity. The median follow-up was 17 mo, and 53% of those with at least 2yr of follow-up (103/193) had a biopsy performed. The 5-yr cumulative incidence of PSA failure was 2.1%, and the incidence of a positive 2-yr treatment biopsy was 12%. Limitations to this report include its retrospective nature and short follow-up time. ConclusionsFavorable short-term outcomes were achieved with high-dose SBRT for low- and intermediate-risk disease. Severe late toxicities were observed and favorable tumor control was found. Patient summaryWe utilized stereotactic body radiotherapy, a form of external beam radiotherapy that delivers highly targeted high-dose treatment to the prostate, to treat over 500 localized prostate cancer patients in five sessions over 1.5 wk. Treatments were well tolerated without significant urinary or rectal side effects. Nearly 90% of those who underwent biopsies after treatment did not demonstrate residual active disease.