A Pilot Trial of Two-Fraction Stereotactic Body Radiation Therapy for Localized Prostate Cancer

Ultra-hypofractionated radiation is a widely adopted treatment for low- and intermediate-risk prostate cancer and is typically given for a duration of five treatments in the United States. There is interest in developing a shorter two-treatment course. We conducted a pilot study of two-fraction ultra-hypofractionated radiation therapy for low- to intermediate-risk prostate cancer to determine safety and preliminary efficacy.

A total of 12 patients were prospectively enrolled in a single-arm pilot study of two-fraction ultra-hypofractionated radiation therapy. Patients were treated with 12.5 Gy in two fractions separated by 2-3 days. All patients had placement of a rectal spacer. Biochemical response was evaluated with prostate-specific antigen (PSA) monitoring, with recurrence defined using the American Society for Therapeutic Radiology and Oncology (ASTRO) Phoenix criteria. Toxicity was graded using the Common Terminology Criteria for Adverse Events (CTCAE) v5.0.

Median follow-up was 4.8 years. This cohort consisted of National Comprehensive Cancer Network (NCCN) intermediate-risk patients (seven NCCN favorable intermediate and five NCCN unfavorable intermediate). The median prostate volume was 30 cc. The median PSA nadir was 0.14 (range <0.01 to 0.82). No patient experienced a biochemical recurrence. No patient experienced grade 2 or worse gastrointestinal (GI) acute or late toxicity. Three of the 12 patients experienced acute grade 2 genitourinary (GU) toxicity, and two of the 12 patients experienced late grade 2 toxicity. No patient experienced grade 3 toxicity.

Two-fraction ultra-hypofractionated radiation to 25 Gy is tolerable with a low rate of long-term toxicity and promising biochemical control. Further research is indicated to evaluate two-fraction regimens for prostate radiation.