FLAME: Investigate the Benefit of a Focal Lesion Ablative Microboost in Prostate Cancer

Rationale: Dose escalation in external-beam irradiation has proven to benefit outcome in local prostate cancer. Randomized trials were performed up to doses of 78 Gy in 2 Gy fractions. Nevertheless, the five-year biochemical relapse rate still was approximately 35% in the high-dose arm. Therefore further dose escalation seems to be required. A feasibility study up to appr. 85 Gy on the entire prostate has already been performed and showed acceptable toxicity when combined with adequate position verification. Higher doses to the entire prostate are expected to increase severe toxicity. As local recurrences only occur at the site of the primary macroscopic tumour area the next step in increasing the dose should be an ablative boost to the macroscopic tumour alone, while electively irradiating the rest of the prostate to the current gold standard dose. Feasibility of this approach has been shown for an ablative dose of 95 Gy to the macroscopic tumour within the prostate.