Eight-Year Prostate Brachytherapy Update Shows Good Results

ORLANDO—Researchers at the Seattle Prostate Institute, University of Washington, and Northwest Hospital have shown excellent progression-free survival in favorable prostate cancer patients with the use of transperitoneal ultrasound-guided brachytherapy as sole treatment. Peter Grimm, DO, presented eight-year follow-up data on more than 400 patients in a poster presentation at the American Society for Therapeutic Radiology and Oncology meeting.

“This is the longest follow-up available for prostate brachytherapy,” Dr. Grimm, of the Seattle Prostate Institute, told Oncology News International.

The study included 403 patients treated consecutively between January 1988 and December 1993. All patients had a histologic diagnosis of prostate cancer. The median age was 69 years (range, 46 to 91), and median follow-up was 53 months (range, 12 to 109 months).

Dr. Grimm stressed the importance of patient selection for brachytherapy as the sole modality. These patients, he said, were selected on the basis of low risk for locally extensive or disseminated disease. The majority (61%) had stage T2a disease; the rest broke down as follows: T1a, 2%; T1b, 3%; T1c, 22%; T2b, 11%; and T2c, 1%. Gleason score at presentation was also considered, with 40% of patients having a Gleason score of 2 to 4; 51%, Gleason 5 to 6; and 9%, Gleason 7 to 10.

All patients underwent permanent transperitoneal seed implant as their sole treatment. None of the patient received adjuvant hormonal therapy. Patients received either iodine-125 with an average of 99 seeds at 0.35 mCi per seed to an MPD (minimum peripheral dose) of 160 Gy, or palladium-103 with an average of 95 seeds at 1.3 mCi per seed to an MPD of 115 Gy.

Multiple Endpoints Examined

Dr. Grimm and his colleagues looked at several endpoints to get a clear perspective on the treatment’s efficacy. “We’re trying to include different ways of looking at the data,” Dr. Grimm said in an interview.

He believes the most sensitive endpoint is biochemical progression-free survival, defined by ASTRO in 1996 as the absence of a consecutive rise in PSA over three or more measurements.

Using the ASTRO definition, the overall biochemical progression-free survival at 8 years in these patients is 86%, Dr. Grimm reported. When looked at by disease stage, this endpoint breaks down as follows: T1a,b, 86%; T1c, 81%; T2a, 90%; T2b, 78%; and T2c, 53%.

By Gleason score, 8-year biochemical progression-free survival is 89% for those with a score of 2 to 6 and 48% for those with a score of 7 to 10.

Finally, by initial PSA level, progression-free survival was 92% for those with initial PSA of 0 to 4 ng/mL; 90% for PSA of 4 to 10 ng/mL; 85% for PSA of 10 to 20 ng/mL; and 50% for PSA over 20 ng/mL.

Dr. Grimm also calculated 8-year survival of those who failed to achieve a serum PSA of less than 1 ng/mL. This figure, 73%, is, of course, lower than the overall figure of 86%. Dr. Grimm said that he finds use of absolute PSA problematic as an endpoint because some patients never reach PSA below 1 and yet are still progression free.

The patients were also divided into high- and low-risk groups and analyzed by an optimized stratification model. The low-risk group had an initial PSA of 10 ng/mL or less and a Gleason score of 6 or less and showed an 8-year biochemical progression-free survival of 92%.

Those considered high risk had an initial PSA greater than 10 ng/mL or a Gleason score greater than 6. Their progression-free survival was 71% at 8 years.

Overall, patients with an initial PSA less than 20 and Gleason score less than 7 (N = 320) had a 91% biochemical progression-free survival at 8 years vs 56% for initial PSA greater than 20 or Gleason score above 6 (N = 40).

Biopsy results obtained from 58% of the patients (N = 232) showed 81% as negative, 5% positive, and 14% indeterminate. Dr. Grimm said that the indeterminate biopsy category was categorized by malignant epithelia exhibiting severe radiation effect accompanied by cellular atypia. These patients, he said, resemble those with negative biopsies biochemically and clinically. “In a previous review, 85% of patients with an indeterminate biopsy have converted to negative.”

Dr. Grimm feels that the results of the clinical update point to permanent seed brachytherapy as being an effective single modality for early-stage prostate cancer. From the various endpoints analyzed, the researchers feel that brachytherapy is equal or superior to surgery or external beam radiation.

“We feel that this control rate is largely due to satisfactory prescribed doses, careful preoperative planning, diligent execution of the preplan, and careful selection of patients for seed implant alone,” he concluded.