ULTRASOUND-GUIDED HIGH-DOSE-RATE CONFORMAL BRACHYTHERAPY BOOST IN PROSTATE-CANCER - TREATMENT DESCRIPTION AND PRELIMINARY-RESULTS OF A PHASE I II CLINICAL-TRIAL/

Purpose: To improve results for locally advanced prostate cancer, a pr ospective clinical trial of concurrent external beam irradiation and f ractionated iridium-192 (Ir-192) high dose rate (HDR) conformal boost brachytherapy was initiated. Methods and Materials: Between November 1 991 and February 1994, 99 implants were performed on 33 patients with prostatic adenocarcinoma at William Beaumont Hospital. Using AJCC stag ing criteria, 9 patients had T2b tumors, 17 patients had T2c tumors, a nd 7 patients had T3 disease. Patients were treated with (a) 45.6 Gy w hole pelvis external irradiation and (b) three HDR fractions of 5.5 Gy each (18 patients) or 6 Gy each (15 patients) to the prostate. Transp erineal needle implants using real-time ultrasound guidance with inter active on-line isodose distributions were performed on an outpatient b asis during weeks 1, 2, and 3 of external irradiation. Acute toxicity was scored using the Radiation Therapy Oncology Group (RTOG) morbidity grading system. Results: This technique of concurrent external pelvic irradiation and conformal HDR brachytherapy was well tolerated. No si gnificant intraoperative or perioperative complications occurred. Thre e patients (9%) experienced Grade 3 acute toxicity (two dysuria and on e diarrhea). All toxicities were otherwise Grades 1 or 2 and were prim arily as expected from pelvic external irradiation. Persistent implant -related toxicities included Grades 1-2 perineal pain (12%) and hemato spermia (15%). Median follow-up time was 13 months. Serum prostatic-sp ecific antigen (PSA) levels normalized in 91% of patients (29 out of 3 2) within 1-14 months (median 2.8 months) after irradiation. PSA level s were progressively decreasing in the other three patients at last me asurement. Prospectively planned prostatic rebiopsies done at 18 month s in the first 10 patients were negative in 9 out of 10 (90%). Conclus ions: Acute toxicity has been acceptable with this unique approach usi ng conformal high dose rate Ir-192 boost brachytherapy with concurrent external irradiation. The initial tumor response as assessed by seria l PSA measurement and rebiopsy is extremely encouraging. Dose escalati on will proceed in accordance with the protocol guidelines. Further pa tient accrual and longer follow-up will allow comparison to other tech niques.