"Give me five" ultra-hypofractionated radiotherapy for localized prostate cancer: non-invasive ablative approach

Ultra-hypofractionated radiotherapy (RT) is given over a shorter time with larger doses with respect to conventional fractionation in patients with localized prostate cancer (PCa). The use of hypofractionation is supported both from the radiobiological point of view (the low α/β-ratio in PCa and dose escalation) and from the rising number of clinical evidences. The aim of this study is to review our data regarding oncological outcomes, namely biochemical progression-free survival (b-PFS) and clinical progression-free survival (c-PFS), acute and long-term toxicities in patients treated with a ultra-hypofractionated RT. A series of 194 patients with clinically localized PCa treated primarily with ultra-hypofractionated RT using image-guided intensity modulated RT (IG-IMRT) at our Institute from 2012 to 2015 was included in this analysis. According to NCCN risk group classification, 65 (33.5%) patients were low risk, 101 (52.1%) intermediate risk, and 28 (14.4%) high risk. Androgen deprivation therapy (ADT) was given to 61 patients (31.4%). A 169 patients (87.1%) received 35 Gy in 5 fractions, while 25 patients (13%) received 32.5 Gy in 5 fractions (usually given in patients with comorbidity). The median duration of the treatment was 10 days (IQR 9-12). Biochemical relapse was defined as a rise of prostate specific antigen (PSA) > 2 ng/ml above nadir. b-PFS, c-PFS, and freedom from gastro-intestinal (GI) and genito-urinary (GU) toxicity curves were calculated by the Kaplan-Meier method. Log-rank test and multivariate Cox models were used to investigate the role RT dose and heterogeneity by NCCN risk groups adjusting for prognostic factors. Data on acute and late term toxicities were collected according to RTOG/EORTC grading system. With a median follow-up of 30 months, 17 patients experienced PSA failure (9%). The 3-year b-PFS was 87% for all patients and rates stratified for the NCCN risk were 94, 82, and 66% for low-, intermediate-, and high-risk groups, respectively. Log-rank tests indicate that biochemical progression was significantly greater for patients with initial PSA (iPSA) greater than 7 ng/ml (P = 0.04), high- and intermediate-risk groups (P = 0.002), low total dose (P = 0.02) and Gleason score (GS) equal or greater than 7 (P = 0.04). No statistically significant association was found with T stage nor ADT. In multivariate analyses, total dose (P = 0.03) and risk groups (P = 0.03) remained significantly associated with recurrence. Acute and late GI and GU toxicity were acceptable. The toxicity of ultra-hypofractionated IG-IMRT in a large clinical cohort of PCa patients was tolerable and confirmed that this treatment is safe and offers excellent tumor control. Moreover, the hypofractionated RT allows to deliver the whole RT over 10 days with a sensible impact in patients' quality of life and potential overall health system and social benefits.