Dose-Escalated Stereotactic Body Radiation Therapy for Patients With Intermediate- and High-Risk Prostate Cancer: Initial Dosimetry Analysis and Patient Outcomes

Abstract

To report the short-term clinical outcomes and acute and late treatment-related genitourinary (GU) and gastrointestinal (GI) toxicities in patients with intermediate- and high-risk prostate cancer treated with dose-escalated stereotactic body radiation therapy (SBRT). Between 2011 and 2014, 24 patients with prostate cancer were treated with SBRT to the prostate gland and proximal seminal vesicles. A high-dose avoidance zone (HDAZ) was created by a 3-mm expansion around the rectum, urethra, and bladder. Patients were treated to a minimum dose of 36.25Gy in 5 fractions, with a simultaneous dose escalation to a dose of 50Gy to the target volume away from the HDAZ. Acute and late GU and GI toxicity outcomes were measured according to the National Cancer Institute Common Terminology Criteria for Adverse Events toxicity scale, version4. The median follow-up was 25months (range, 18-45months). Nine patients (38%) experienced an acute grade 2 GU toxicity, which was medically managed, and no patients experienced an acute grade 2 GI toxicity. Two patients (8%) experienced late grade 2 GU toxicity, and 2 patients (8%) experienced late grade 2 GI toxicity. No acute or late grade ≥3 GU or GI toxicities were observed. The 24-month prostate-specific antigen relapse-free survival outcome for all patients was 95.8% (95% confidence interval 75.6%-99.4%), and both biochemical failures occurred in patients with high-risk disease. All patients are currently alive at the time of this analysis and continue to be followed. A heterogeneous prostate SBRT planning technique with differential treatment volumes (low dose: 36.25Gy; and high dose: 50Gy) with an HDAZ provides a safe method of dose escalation. Favorable rates of biochemical control and acceptably low rates of acute and long-term GU and GI toxicity can be achieved in patients with intermediate- and high-risk prostate cancer treated with SBRT.