Stereotactic body radiation therapy for low and intermediate risk prostate cancer—Results from a multi-institutional clinical trial

• Results of a multi-institutional study of stereotactic body radiation therapy for prostate cancer are reported.
• Doses up to 47.5 Gy in five fractions resulted in high control with acceptable toxicity.
• Fifty gray in five fractions was associated with an increase in late high grade toxicity.
• Three and five year biochemical control rates are 100 and 98.6% respectively.

BackgroundWe report the outcome of a phase I/II clinical trial of stereotactic body radiation therapy (SBRT) for low (LR) and select intermediate risk (IR) prostate cancer (PCa) patients.Patients and methodsEligible patients included men with prostate adenocarcinoma with Gleason score 6 with PSA ≤ 20 or Gleason 7 with PSA ≤ 15 and clinical stage ≤ T2b. For the phase I portion of the study patients in cohorts of 15 received 45, 47.5, or 50 Gray (Gy) in five fractions. Since the maximally tolerated dose was not met in the phase I study, an additional 47 patients received 50 Gy in five fractions in the phase II study. Toxicity using Common Toxicity Criteria for Adverse Events v. 3.0, quality of life, and outcome data was collected.ResultsA total of 91 patients are included for analysis; 63.7% had NCCN IR and 36.3% had LR PCa. At a median follow up of 54 months the actuarial freedom from biochemical failure was 100% at 3 years and 98.6% at 5 years. Actuarial distant metastasis free survival was 100% at 3 and 5 years. Overall survival was 94% at 3 years and 89.7% at 5 years with no deaths attributed to PCa. Acute and late urinary grade ≥ III toxicity occurred in 0% and 5.5% of patients, respectively. Gastrointestinal (GI) acute and late toxicity of grade ≥ III occurred in 2% and 7% of patients, respectively. A total of four men experienced grade IV toxicity (three GI, one genitourinary).ConclusionSBRT treatment results in excellent biochemical control rates at 5 years for LR and IR PCa patients although doses greater than 47.5 Gy in five fractions led to increased severe late toxicity.