Linac-based stereotactic body radiation therapy for low and intermediate-risk prostate cancer : Long-term results and factors predictive for outcome and toxicity.

Abstract

Stereotactic body radiation therapy (SBRT) is considered an effective and safe treatment in patients with low- and intermediate-risk prostate cancer (PC). However, due to alack of long-term follow-up and late toxicity data, this treatment is not universally accepted. The present study aimed to evaluate outcome and early and late toxicity in acohort of patients with low- and intermediate-risk PC treated prospectively with linear accelerator (linac)-based SBRT. Patients with low- or intermediate-risk (NCCN criteria) PC were included. All patients received linac-based SBRT to 35 Gy in 5fractions delivered on alternate days. Endpoints were toxicity, biochemical relapse-free survival (BRFS), metastatic progression-free survival (mPFS), and overall survival (OS). From 2012 to 2018, 178 patients were treated. Median baseline prostate-specific antigen (iPSA) was 6.37 ng/ml (range 1.78-20). Previous transurethral resection of the prostate (TURP) was present in 23 (12.9%) patients. Median follow-up was 58.9 months (range 9.7-89.9). BRFS rates at 1, 3, and 5years were 98.3 (95% confidence interval, CI, 94.7-99.4%), 94.4 (95%CI 89.4-97), and 91.6% (95%CI 85.4-95.2), respectively. In univariate analysis, performance status (PS), iPSA, and nadir PSA (nPSA) were correlated with BRFS. In multivariable analysis iPSA and nPSA remained significant. BRFS rates at 5years were 94.9% (95%CI 86.8-98) for International Society of Urological Pathology (ISUP) grade group1, 93.2% (95%CI 80.5-97.7) for ISUP group2, and 74.8% (95%CI 47.1-89.5) for ISUP group3. At 1, 3, and 5years, mPFS rates were 98.8 (95%CI 95.5-99.7), 96.2 (95%CI 91.9-98.3), and 92.9% (95%CI 87.2-96.2), respectively; OS rates were 100, 97.2 (95%CI 92.9-98.9), and 95.1% (95%CI 90-97.6), respectively. One (0.56%) case of grade3 acute genitourinary (GU), one case of acute gastrointestinal (GI), and one case of grade3 late GU toxicity were observed. GI toxicity positively correlated with prostate volume. At long-term follow-up, linac-based SBRT continues to be avalid option for the management localized PC. Biochemical control remains high at 5years, albeit with some concerns regarding the optimal schedule for unfavorable intermediate-risk PC. Considering the excellent prognosis, patient selection is crucial for prevention of severe late toxicity.