Prostate Stereotactic Body Radiation Therapy With a Focal Simultaneous Integrated Boost: Acute Toxicity and Dosimetry Results From a Prospective Trial

Abstract Purpose To report the early toxicity results of a prospective clinical trial of prostate stereotactic body radiotherapy (SBRT) to the entire prostate with a simultaneous integrated boost (SIB) to MRI-defined focal lesions. Materials and Methods Eligible patients included men with biopsy-proven prostate adenocarcinoma stage T1c-T2c, Gleason score ≤ 7, and prostate specific antigen ≤ 20 ng/mL who had at least one focal lesion visible on MRI and total prostate volume no greater than 120 cc. SBRT consisted of a dose of 36.25 Gy to the entire prostate with an SIB of 40 Gy to the MRI-defined lesions, delivered in 5 fractions. The primary purpose of the study was to confirm the feasibility of treatment planning/delivery, and to estimate the rate of urinary retention requiring placement of a Foley catheter within 90 days of treatment. This study was to be considered successful if urinary retention occurred in no more than 15% of cases, with a planned enrollment of at least 25 patients. Results A total of 26 men were enrolled and all underwent SBRT as planned. Twenty (77%) had intermediate risk features and the remainder were low risk. A treatment plan was able to be developed that met the protocol defined goals for all cases. Two (7.7%) patients developed acute urinary symptoms requiring temporary placement of a Foley catheter. No grade 3+ toxicity events were observed. Conclusion Planning and delivery of prostate SBRT with a whole prostate dose of 36.25 Gy and a focal 40 Gy SIB is feasible. Early follow-up suggests that this treatment is not associated with undue morbidity.