High dose-rate afterloading 192Iridium prostate brachytherapy: feasibility report

RESULTS from localized prostate cancer series using seed implants have been most encouraging. However, with current techniques, inadequate dosimetry sometimes occurs. Remote afterloading high dose rate 192Iridium brachytherapy (HDR-Ir192) theoretically remedies some potential inadequacies of seed implantation by performing the dosimetry after the needles are in place. This study was undertaken to determine the feasibility of incorporating multifractionated HDR-Ir192 in the brachytherapy management of prostate carcinoma.

From October 1989 to August 1995, 104 patients were treated with a combination of multifractionated HDR-Ir192 and external beam. Patients ranged in age from 48-78 years, with a mean of 68.6 years. By TNM clinical stage, there were 1 T1b, 31 T1c, 28 T2a, 24 T2b, 9 T2c, 8 T3a, and 3 T3c lesions. For the group, the mean initial pretreatment PSA was 12.9 ng/ml (median 8.1), with 90% of the patients having had a pretreatment PSA greater than a normal value of 4.0 ng/ml. Patients with prostate volumes up to 105 cc were implanted. Treatment was initiated with perineal needle placement using ultrasound guidance. A postoperative CT scan was obtained to provide the basis for treatment planning. Four HDR-Ir192 treatments were given over a 40-h period, with a minimal peripheral dose (MPD) ranging from 3.00 to 4.00 Gy per fraction over the course of this study. Two weeks later, external beam radiation was added using 28 fractions of 1.80 Gy daily, to a dose of 50.40 Gy.

Follow-up ranged from 10 to 89 months, with a mean of 46 months and median of 45 months. At various follow-up points, the patient numbers at risk were: 1 year, 101; 3 years, 69; 5 years, 28. The technique proved to be uniformly applicable to a wide range of prostate volumes and was very well tolerated by patients. Nearly all significant late in-field treatment complications were genitourinary in nature. Of the patients, 6.7% developed urethral strictures that were readily manageable. Changes in technique implemented in 1993 appear to have significantly lessened the incidence of this complication. Two patients developed significant uropathy within the first treatment year, but both resolved; 1 of these 2 patients had a prior TURP. Other bladder or rectal complications have been minimal. Using PSA progression as a marker of tumor response, approximately 84% of patients whose initial PSA was less than 20 ng/ml were free of progression at 5 years by actuarial analysis.

We found the use of transperineal ultrasonography, postimplant CT-based dosimetry, coupled with adjustable dose delivery inherent to remote afterloading technology, to give unparalleled control in performing this complex brachytherapy task. Thus, it may be advantageous in certain clinical situations where the resultant MPD is needed to reliably cover the target volume, such as in patients with carcinomas at base locales, when the possibility of moderate to extensive intraprostatic tumor exists, and in patients with large glands. Early PSA data suggest that it may be effective as a definitive treatment with rates of adverse late tissue effects that are acceptable using current technique and doses described herein. Longer follow-up is needed to ascertain its position among the various treatment regimens for prostate carcinoma.