Implementation of SBRT as a Rescue Technique for Reirradiation of Local Recurrence of Prostatic Cancer

Background: External beam radiation therapy and brachytherapy are very efficient treatment modalities for localized prostate cancer, although more than 30% of the patients would experience a biochemical recurrence within 10 years. Among these patients, about 20% would present a local recurrence, and optimal management of locally recurrent prostate cancer after definitive radiation therapy is still challenging. In this scenario the most common retreatment option is androgen deprivation therapy, which cannot be considered as a radical treatment. Surgery, as a radical salvage modality and other focal treatments such as cryotherapy, high-intensity focused ultrasound (HIFU), and brachytherapy can be offered to highly selected patients. More recently, the development of SBRT (stereotactic body radiation therapy), allows to deliver higher ablative dose of radiation to a smaller target volume with better sparing of surrounding critical organs at risk and can be an encouraging alternative for patients with a postirradiation relapse of prostate cancer. To date, the number of publications in this fields considerably low, and results are inconclusive mainly due to the limited number of patients treated and the lack of randomized clinical trials.

Hypothesis: The intensification of focal doses of radiation with SBRT, in a rescue scenario after a post-irradiation relapse of prostate cancer, can be a safe and effective local treatment.

Objectives: Primary: The purpose of this research study is to implement SBRT for the treatment of post- irradiated local recurrence prostate cancer. Secondary: The aim of this study was to evaluate the tolerance and the effectiveness (biochemical control, disease free survival and survival) of SBRT in previously irradiated prostate cancer relapses.

Material, Methods and Stages of development: A) Selection of the patients at the multidisciplinary tumor board. Eligibility criteria: Patients with a biochemical recurrence (PSA level > 2 ng/ml) and a proven local recurrence of prostate cancer previously irradiated (proven by biopsy or positive 18 F-Choline- PET- CT or PSMA PET-TC). With good performance status and absence of previous rectal or urinary radiation induced toxicity (normal cystoscopy and rectoscopy).

B) Establish treatment protocol: CT simulation and immobilization will be described. GTV, CTV and PTV margins, total dose, fractionation and constraints of organs at risk will be defined. IMRT or VMAT will be performed with daily IGRT.

C) Follow up to evaluate toxicity, local control and survival will be performed every 3 months during the first 2 years. Evaluation of clinical tolerance and clinical response will be performed, with a quality of life questionnaire, and PSA levels. 18 F-Choline PET-CT or PSMA PET-TC will be performed in case of biochemical failure (PSA levels> 2 ng/ml)

D) Previous approval of the Local Research Ethics Committee.