The TEMPOS-GEniToUrinary Group (GETUG) study is a multicenter, medico-economic study comparing brachytherapy to SBRT in low and intermediate risk prostate cancer, particularly focused on the issue of erectile dysfunction. A total of 240 potent patients are randomized in two arms. The experimental arm consists of SBRT delivering 7.25 Gy per fraction, in five fractions, corresponding to a total dose of 36.25 Gy to the prostate. The control arm consists of brachytherapy by Iodine 125 delivering 144 Gy to the prostate. The main objective of this health economics study is to perform a cost-utility analysis of SBRT compared to standard Iodine 125 brachytherapy in low-risk prostate cancer, 3 years after treatment. The endpoint is the Incremental Cost-Utility Ratio (ICUR) between SBRT and brachytherapy as primary criterion, expressed in cost per quality adjusted life year (QALY) gained. Cost-effectiveness analyses are performed as secondary objective with Incremental Cost-Effectiveness Ratios (ICERs) expressed as cost per erectile dysfunction avoided and cost per Life Year Gained. A long term evaluation is also performed, including a cost-utility, cost-effectiveness and budget impact analysis at 5 years, a comprehensive assessment of the erectile dysfunction up to 5 years after treatment, an evaluation of acute and late genito-urinary (GU) and Gastro-Intestinal (GI) toxicities, and of quality of life up to 5 years after treatment. Eight patients/year/center are expected to be recruited in 2 years in about twenty participating centers. In total, to our knowledge, this study will be the first health economic evaluation which compares SBRT versus Iodine 125 brachytherapy in low risk and intermediate risk prostate cancer. Both cost-utility and cost-effectiveness analyses will also provide useful and complementary information to decision makers in order (i) to recommend the best strategy to adopt; (ii) to estimate the budget impact on the French National Health Insurance of the generalization of the cost-effective strategy. Finally, this study will allow to assess and compare accurately the erectile dysfunction after both treatment modalities.