SAN DIEGO—Higher radiation doses are critical to optimizing long-term outcomes following brachytherapy for prostate cancer (PCa), a study presented at the American Urological Association 2016 annual meeting suggests.

In a study of 1,754 men who received brachytherapy and were followed up for a median of 9.5 years (range 5–22 years), patients who received a biologic effective dose (BED) less than 170 Gy2 had a 2.27 times increased risk of PCa-specific mortality compared with those who received a BED of 170 Gy2 or higher, investigators Nelson N. Stone, MD, and Richard G. Stock, MD, of the Icahn School of Medicine at Mount Sinai in New York, reported.

The study also found that higher clinical stage and Gleason score adversely impact long-term outcomes following brachytherapy. Patients with higher clinical stage had a significant 35% increased risk of biochemical failure and 70% increased risk of PCa-specific mortality at 15 years compared those who had lower clinical stages, according to investigators. Patients with a Gleason score of 7 or higher had a significant 28% increased risk of biochemical failure and 89% increased risk of PCa-specific mortality compared with patients who had lower Gleason scores.

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The researchers defined biochemical failure using the Phoenix definition (nadir PSA plus 2 ng/mL).

The study population included 796 patients (43.8%) with low-risk, 668 (38.1%) with intermediate-risk, and 290 (16.6%) with high-risk cancers. Low-risk patients were treated with brachytherapy implants alone or implants plus hormone therapy (in patients with prostates larger than 50 cc) for a median of 3 months. Intermediate-risk patients were treated with implants plus hormone therapy (median 6 months) or implants plus external beam radiation therapy (EBRT). High-risk patients were treated with implants plus hormone therapy (median 9 months) plus EBRT. The investigators converted the radiation doses from implants and EBRT to the biologic effective dose (BED). They classified BED as low (less than 150 Gy2), intermediate (150–200 Gy2), and high (greater than 200 Gy2).

Overall, the biochemical freedom from failure (BFF) rates at 5, 10, and 15 years were 99.9%, 92.4%, and 70.4%, respectively. The BFF rates at 15 years for the low-, intermediate-, and high-risk patients were 77.2%, 69.5%, and 53.8%, respectively.

The cohort as a whole had a 15-year cancer-specific survival rate of 94.1%. The rates were 97.5%, 97%, and 83.7% for patients with low-, intermediate-, and high-risk disease, respectively. Patients had a mean survival time of 21 years.

“This is the first study to demonstrate that higher radiation dose in men treated with prostate brachytherapy results in improved cancer-specific survival in low-, intermediate-, and high-risk prostate cancer,” Dr Stone said.

The 15-year BFF for patients who received low, intermediate, and high BED was 74%, 87%, and 91.8%, respectively, for patients with low-risk disease, 49.8%, 83.9%, and 88.7%, for those with intermediate-risk disease, and 40.7%, 63.1%, and 74.8% for those with high-risk disease, according to the investigators.