Hypofractionated Radiotherapy for Prostate Cancer

External beam radiotherapy (RT) is one of the standard curative treatment options for patients with prostate cancer (PC). Several randomised trials have shown excellent long-term biochemical outcome with higher radiation doses. Nowadays, RT for PC commonly consists of delivering 74-80 Gy in 2 Gy fractions, resulting in an overall treatment time of 7-8 weeks. The sensitivity of different tissues to fractionation changes can be quantified through the alpha/beta ratio in the linear-quadratic model. Dose-response analysis of PC patients treated with both external beam RT and brachytherapy has led to the hypothesis that the alpha/beta ratio of PC is lower than for most other tumors and approaches a value characteristic of late responding tissues. Values between 1.2 and 3.9 Gy have been calculated. If the alpha/beta ratio of PC is indeed low, then hypofractionating RT treatments can theoretically maintain high bioequivalent tumor doses, shorten overall treatment time and decrease late toxicities.The advantages in terms of patient convenience and treatment cost are obvious. There is level I evidence that shows that hypofractionated radiotherapy schedules have at least equivalent biochemical outcome with only a small increase in acute but not late toxicity when compared to conventional fractionation RT schedules. Results on different hypofractionation schedules have been reported, however the optimal hypofractionation is not clear so far. In this randomised trial we would like to compare 2 different radiotherapyschedules: 16 fractions à rato of 4 fractions a week versus 25 fractions à rato of 5 fractions a week. The incidence on acute toxicity and early late toxicity (i.e. within 2 year post radiotherapy) and the impact on quality of life will be registrated and compared. The study will be performed in 2 stages. For stage 1, sample size was calculated to rule out an upper limit of 40% of patients with RTOG grade 2 or worse bowel (GI) complications with an expected rate of