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

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).

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.

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.

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.