Short-term high precision radiotherapy for early prostate cancer with concomitant boost to the dominant lesion: ad interim analysis and preliminary results of Phase II trial AIRC-IG-13218.

OBJECTIVE: To report preliminary results of a cutting edge extreme hypofractionated treatment with concomitant boost to the dominant lesion for patients with early stage prostate cancer (PCa).
METHODS: AIRC-IG-13218 is a prospective Phase II trial started in June 2015. Patients with low and intermediate risk PCa who met the inclusion criteria underwent extreme hypofractionated radiotherapy to the prostate (36.25 Gy in 5 fractions) and a simultaneous integrated boost to the dominant intraprostatic lesion (DIL) to 37.5 Gy. The DIL was identified by a multiparamentric MRI (mpMRI) co-registered with planning CT. Toxicity was assessed according to CTCAE v4.0 and RTOG/EORTC criteria. The preliminary evaluation of the first 13 patients was required to confirm the feasibility of the treatment before completing the enrollment of 65 patients.
RESULTS: The first 13 patients completed the treatment between June 2015 and February 2016. With a median clinical follow-up of 17 months (range 11-26), no Grade 3 or 4 early toxicity was reported.
CONCLUSIONS: Our preliminary data about early toxicity of an extreme hypofractionated schedule with concomitant boost on the DIL are encouraging. The higher number of patients expected for the trial and a longer follow-up are needed to confirm these results. Advances in knowledge: The use of mpMRI to identify and boost the DIL is an innovative and interesting approach to PCa. Our preliminary findings suggest that dose escalation using DIL boost and extremely hypofractionated radiotherapy regimens might be a safe approach, allowing for short and effective treatment of organ-confined PCa.