Is Low-Dose-Rate Interstitial Brachytherapy for Patients with Large Prostates (>60 cc) Safe and Effective?

Purpose: The purpose of this study was to review the dosimetry and efficacy of our single physician, single-institution experience using low-dose-rate (LDR) brachytherapy in patients with large volume prostate glands (>60 cc). Materials and Methods: Out of a total of 925 consecutive patients treated with LDR interstitial brachytherapy implants for prostate cancer at Beth Israel Medical Center between 1998 and 2008, 68 patients were identified as having a pre-implant ultrasound volume of more than 60cc (mean, 71.9 cc; median, 67.9 cc; range, 60.2-117.0 cc). Forty-eight patients received LDR brachytherapy as a boost (108 Gy) before or after conformal external beam radiation therapy, and the remaining 20 patients received LDR brachytherapy alone (144 Gy). Sixty-seven percent of patients received neoadjuvant, concurrent, and adjuvant androgen deprivation therapy. Three patients were in the NCCN-high risk group. 24 were classified as NCCN-intermediate risk, and 41 as NCCN-low risk. Post-implant dosimetry was obtained on the day of implant for all patients, with a single implanting physician performing all contours. Results: The median D90 (minimal dose to 90% of the prostate) was 105% of prescription dose (range, 75-135%), the median V100 (volume receiving 100% of the dose) was 93% (range, 74-100%) and the median V150 was 51% (range, 22-79%). The median volume of rectum receiving 100% of the prescription dose was 0.15 cc. The median V150 for the urethra (volume receiving 150% of the dose) was 8%. Long-term followup data (minimum 1 year followup) was available for 54 out of the 68 patients. With a median followup of 36 months, there have been three biochemical failures (two in the low risk group, one in the intermediate risk group). Four patients (6%) required temporary placement of a urinary catheter for acute obstructive symptoms, with one patient (who had multiple sclerosis) developing a fistula requiring permanent suprapubic catheterization. There have been no cases of acute or long term Grade 2 gastrointestinal toxicity. Conclusions: We present one of the largest series evaluating efficacy and toxicity outcomes after LDR brachytherapy performed in patients with prostatomegaly. Our findings demonstrate that large prostate volume is not a contraindication to LDR brachytherapy. Furthermore, excellent dosimetric coverage is routinely achievable without incurring significant acute and long-term toxicity.