Linac based SBRT for prostate cancer in 5 fractions with VMAT and flattening filter free beams: preliminary report of a phase II study.

BACKGROUND: To evaluate the feasibility and early side effects of a short course hypo-fractionated SBRT programme with Volumetric Modulated Arc Therapy (VMAT) and Flattening Filter Free (FFF) beams. METHODS: A prospective phase I-II study, started on February 2012. Inclusion criteria were: age <= 80 years, WHO-PS <= 2, PSA <= 20 ng/ml, histologically proven prostate adenocarcinoma, T1-T2 stage, no distant metastases, no previous surgery other than TURP, no malignant tumours in the previous 5 years, IPSS 0--7. The schedule was 35Gy in 5 alternative days. SBRT was delivered with RapidArc VMAT, with 10MV FFF photons. Toxicity assessment was performed according to CTCAE v4.0 scale. EPIC questionnaires assessed Quality-of-Life.. Neo-adjuvant/concomitant hormonal-therapy was prescribed according to risk classification. SpaceOARTM gel was optionally implanted to increase the separation space between the prostate and the rectal wall. RESULTS: Median follow-up was 11 months (range: 5--16); 40 patients were recruited in the protocol and treated.. According to NCCN criteria, 26/40 patients were low-risk and 14/40 were intermediate risk. Median age was 70 years (56--80), median initial PSA was 6.25 ng/ml (0.50-13.43 ng/ml). Median Gleason score was 6 (6--7). All patients completed the treatment as programmed (median 11.8 days (9--22). Acute Toxicities were as follow: Rectum G0: 30/40 cases (75%); G1: 6/40 (15%); G2: 4/40 (10%). Genito-urinary: G0: 16/40 (40%); G1: 8/40 (20%); G2: 16/34 (40%). In two G2 urinary retention cases, intermittent catheter was needed. No acute G3 or greater toxicity was found. Median treatment time was 126 sec (120--136). SpaceOARTM was implanted in 8 patients. PSA reduction from the pre-treatment value of the marker was documented in all patients. CONCLUSIONS: Early findings suggest that SBRT with RapidArc and FFF beams for prostate cancer in 5 fractions is feasible and tolerated in acute setting. Longer follow-up is needed for assessment of late toxicity and outcome.