Phase II Randomized Trial of Radiation Therapy in Oligometastatic mCRPC Prostate Cancer (ARTO)

This phase II randomized trial was designed to evaluate the difference in PSA response rate between the experimental arm (AA+SBRT) and control arm (AA). PSA response will be defined as a post-treatment decrease \> 50% from baseline measured within 6 months. Study design This is a phase II randomized multicenter study in patients affected by oligo ¬mCRPC, treated with standard of care (GnRH agonist or antagonist plus abiraterone acetate and prednisone) and randomized to receive SBRT to all sites of disease. Patients will be randomly assigned in a 1:1 ratio to both treatment, stratified by Centre, Performance Status, and number of metastases. Randomization will be performed the same day of the baseline evaluation (+/-3 days). Planned size of the overall study population is 174 patients, 87 for each arm. The study will include a screening phase and a treatment phase. The screening phase allows for assessment of subject eligibility, demographics, PSA, testosterone, comorbidities and current drug therapies up to 45 days prior to randomization. The treatment phase consists of systemic treatment with abiraterone acetate 1000 mg daily and prednisone 10 mg daily, plus GnRH agonist or antagonist (control arm). Furthermore, the patients in the experimental arm will receive SBRT to all metastatic lesions. SBRT will be delivered in 1 to 5 fractions, and the dose and fractionation schedule will depend on the size and location of the lesion and the surrounding normal tissue constraints in accordance with AAPM Task Group 101 recommendations \[19\]. Considering an Alfa/beta of 3, a BED3 \> 100 Gy is recommended. The total planned duration of the study is 40 months, consisting in 28 months enrollment period, during which patients will perform the screening and will begin standard of care treatment with or without SBRT and later phase of 12 months in which patients will continue the treatment with standard of care and will be submitted to periodic checks every 3 months.