Dose escalation to the DIL(s) will be performed in the traditional Phase I 3+3 design. Patients will be treated in four cohorts (three patients per dose level) starting with a dose of 9 Gy to the DIL(s). If no dose limiting toxicity (DLT), defined below, is observed after 90 days, then an additional three patients will be entered at the next dose level. Dose to the DIL(s) will be escalated at 1 Gy increments until DLT is observed or if maximum dose level (60 Gy in 5 fractions of 12 Gy) is reached with no observed DLT. If one of the three patients experience a DLT at a particular dose level an additional three patients will be enrolled at that level. If two or more patients experience a DLT a lower dose level will be explored to define the maximum tolerated dose (MTD). The three patients within any cohort can be enrolled simultaneously or sequentially without any waiting period among them.

The aim is to perform treatment planning to compute the highest feasible simultaneous boosting dose to the intraprostatic lesion while respecting normal tissue dose constraints. Patients will be treated with MR-guided localization and adaptive planning techniques.

The study aims to evaluate the safety and feasibility to employ a simultaneous integrated boost to MRI detected dominant intraprostatic lesion(s) during SBRT

Dose and volume data will be collected and correlated with treatment-related side effects and quality of life data.