Phase II study of accelerated Linac-based SBRT in five consecutive fractions for localized prostate cancer.

AIM: The goal was to evaluate feasibility, side effects and biochemical no evidence of disease (bNED) after stereotactic body radiation therapy (SBRT) delivered on 5 consecutive days for localized prostate cancer (PC).

METHODS: The study was approved by the ethical committee and started in March 2014. Inclusion criteria were age ≤85 years, WHO performance status ≤2, histologically proven adenocarcinoma, low-intermediate risk, no previous surgery (except transurethral resection of the prostate), and a pre-SBRT International Prostatic Symptoms Score of 0-7. The radiotherapy regimen consisted of 35 Gy for low-risk and 37.5 Gy for intermediate-risk PC in 5 consecutive fractions.

RESULTS: At the time of the analysis, 52 patients were recruited to the study (median age 73 years, range 55-83 years; median follow-up 34 months, range 12-49 months; 34 patients low-risk and 18 intermediate risk). The median initial prostate-specific antigen (PSA) was 5.9 ng/ml (range 1.8-15.7). Acute genitourinary (GU) toxicity was G0 (grade 0) 36/52 (69%), G1 11/52 (21%), G2 5/52 (10%), while acute rectal (GI) toxicity was G0 43/52 (83%), G1 8/52 (15%), G2 1/52 (2%). No acute toxicity ≥G3 was recorded. At the time of analysis late GU and GI toxicities were as follows: GU-G0 43/52 (83%), GU-G1 7/52 (13%), GU-G2 2/52 (4%); GI-G0 48/52 (92%), GI-G1 2/52 (4%), GI-G2 2/52 (4%). No late toxicities ≥G3 were recorded. bNED was 98%. One patient with intermediate PC had distant progression.

CONCLUSIONS: Accelerated SBRT for low-intermediate PC is feasible and well tolerated with comparable oncological outcome as described for other series with the same RT technique but treatment delivery on every other day. Longer follow-up is needed to the assess late toxicity profile and long-term clinical outcome.