Urethrogram-Directed Stereotactic Body Radiation Therapy for Clinically Localized Prostate Cancer in Patients with Contraindications to Magnetic Resonance Imaging

Purpose: Magnetic resonance imaging (MRI)-directed stereotactic body radiation therapy (SBRT) has been established as a safe and effective treatment for prostate cancer. For patients with contraindications to MRI, CT-urethrogram is an alternative imaging approach to identify the location of the prostatic apex to guide treatment. This study sought to evaluate the safety of urethrogram-directed SBRT for prostate cancer. Methods: Between February 2009 and January 2014, 31 men with clinically localized prostate cancer were treated definitively with urethrogram-directed SBRT with or without supplemental intensity modulated radiation therapy (IMRT) at Georgetown University Hospital. SBRT was delivered either as a primary treatment of 35-36.25 Gray (Gy) in 5 fractions or as a boost of 19.5 Gy in 3 fractions followed by supplemental conventionally fractionated intensity modulated radiation therapy (45-50.4 Gy). Toxicities were recorded and scored using the Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v.4.0). Results: The median patient age was 70 years with a median prostate volume of 38 cc. The median follow-up was 3.7 years. The patients were elderly (Median age = 70), and comorbidities were common (Carlson Comorbidity Index > 2 in 36%). 71% of patients utilized alpha agonists prior to treatment, and 9.7% had prior procedures for benign prostatic hyperplasia (BPH). The 3-year actuarial incidence rates of > Grade 3 GU toxicity and > Grade 2 GI toxicity were 3.2% and 9.7%, respectively. There were no Grade 4 or 5 toxicities. Conclusions: MRI is the preferred imaging modality to guide prostate SBRT treatment. However, urethrogram-directed SBRT is a safe alternative for the treatment of patients with prostate cancer who are unable to undergo MRI.