Comparative radiobiological analysis and preliminary results of Ultra hypofractionated accelerated radiotherapy for low-risk prostate cancer patients

Purpose: Moderately accelerated hypofractionation (HypoAR) has been recently established as a standard radiotherapy scheme for low-risk prostate cancer. The application of ultra-hypofractionated regimens (ultra-HypoAR), with fraction size above 5 Gy, is also widely tested. Methods: We applied Image Guided Radiation Therapy (IGRT) ultra-HypoAR delivered with Volumetric Modulated Arc Therapy (VMAT) technique in low-risk prostate cancer patients (5.75 Gy/fraction, 40.25 Gy total dose, two fractions per week). A comparative radiobiological analysis of Dose-Volume Histograms (DVH) obtained for target volumes and organs at risk was performed, investigating the advantages and disadvantages of ultra-HypoAR and conventional radiotherapy regimens (CRT). Early clinical results on efficacy and toxicity are also reported. Results: We calculated the Normalized Total Dose (NTD) and NTD with time correction (NTD_T)-based biological Dose-Volume Histograms (bDVH) for bladder and rectum tissue late effects (alpha/beta=4 Gy) and early effects (alpha/beta=10 Gy). Ultra-HypoAR produced a significantly lower biological dose burden than CRT, for both early and late responding tissue components of the bladder and rectum, whether calculated for time-correction or not (p