Long Term Outcomes of a Novel Five Fraction Hypofractionated Protocol for Low Risk Prostate Cancer

Abstract

Extreme hypofractionation for prostate cancer is the delivery of large doses of radiation ( > 5 Gy) in a few fractions. The potential advantages of an extreme hyprofractionated regime are improved tumour control, minimal acute and late toxicities, and decreased treatment visits. We report the long term toxicities, biochemical and pathological outcomes of a prospective trial of low risk prostate cancer treated with a five fraction hypofractionated radiotherapy regime. A phase I/II study in which patients with low risk localized prostate cancer received 35 Gy in 5 fractions, once a week over 29 days. Treatment was delivered on standard linear accelerators with intensity modulated radiotherapy (IMRT) using daily imaging guidance and gold seed fiducial markers. Post-treatment long term follow up occurred every 6 months up to 5 years. Late toxicity was scored using Radiation Therapy Oncology Group (RTOG) late morbidity scoring criteria. Biochemical control (BC) was defined by the Phoenix definition (nadir + 2 ng/ml). Post-treatment biopsies were obtained at 3 years. As of May 2012, 84 patients have completed treatment with a median follow-up of 50 months (range 12 - 60 months). Median age was 67 years and median baseline PSA was 5.3 ng/ml. The following long term toxicities were observed: Grade 2: 4.7% GI, 4.7% GU, Grade 3+: 1% GI, 1% GU. Biochemical control was observed in 98% of patients. The one patient who has biochemical failure has a history of prostatitis and has a reported negative biopsy. Ninety-six percent were biopsy negative post-treatment. This novel technique of delivering a five fraction extreme hypofractionated schedule of radiotherapy is feasible, well tolerated and shows excellent pathologic and biochemical control for early risk prostate cancer.