Radiation dose key to lasting brachytherapy effect in treating prostate cancer

Key Points

Chicago-Permanent brachytherapy's long-term success in prostate cancer depends on delivery of a high biological effective dose (BED) of radiation, data from more than 2,000 cases showed.

Freedom from biochemical failure, local control, and cause-specific survival improved as BED increased, and BED had a significant association with all three outcomes. Patients in all risk categories benefited from a high BED, according to the report, which was presented at the AUA annual meeting.

"Long-term oncologic outcomes with permanent prostate brachytherapy were excellent, but a high biologic effective dose has to be delivered for successful biochemical freedom from failure, local control, and cause-specific survival," said Nelson N. Stone, MD, clinical professor of urology at Mount Sinai School of Medicine in New York.

Patients were grouped by BED: ≤150 Gy, >150 to 200 Gy, and >200 Gy. Dr. Stone reported that 526 patients (26.6%) had 2-year multi-core prostate biopsy, which was repeated yearly if it read positive or in the case of a rising PSA level.

Median PSA was 7.1 ng/mL and ranged from 0.6 to 300 ng/mL. About two-thirds of the patients (68.9%) had clinical stage ≤T2a, and a similar proportion (67.6%) had Gleason score <7. Risk characteristics were low in 964 patients (45.7%), intermediate in 499 (23.6%), and high in 648 (30.7%). The median follow-up was 6 years and ranged from 2 to 17 years. The median BED was 198 Gy, with a range of 15.1 to 292 Gy.

At 12 years, biochemical freedom from failure was 78.6%, freedom from metastases was 95.2%, and cause-specific survival was 94.5%. Analysis by BED revealed a biochemical freedom from failure of 87.3% in patients who received a BED >200 Gy, 83.6% when the BED was >150 to 200 Gy, and 59% when the BED was 150 Gy or less. Analysis by patient risk showed BED was a significant predictor of biochemical freedom from failure regardless of baseline risk (p=.012 to p<.001).

The proportion of patients with positive biopsy results decreased from 21.5% among patients who received the lowest BEDs, to 5.6% for the intermediate BEDs, to 2.1% for BED >200 Gy (p<.001). The 12-year biochemical freedom from failure rate was 78% in patients with negative biopsies versus 42% for those with positive biopsies (p<.001).

In a regression analysis of predictors of cause-specific survival, only Gleason score (p=.000) and BED (p=.027) emerged as statistically significant factors.

Dr. Stone is an owner of Prologics, LLC.