CONFORMAL PROSTATE BRACHYTHERAPY - INITIAL EXPERIENCE OF A PHASE-I PHASE-II DOSE-ESCALATING TRIAL/

Purpose: To improve treatment results on prostatic adenocarcinoma, con formal radiation therapy (CRT) has been used. Two major drawbacks of e xternal CRT are: (a) internal organ motion/daily set-up variations, an d (b) exclusion of several patients for CRT based on poor geometrical relationships as identified by three dimensional (3D) treatment planni ng. To overcome the above problems, we began the first prospective Pha se I/II dose-escalating clinical trial of conformal brachytherapy (CB) and concurrent external beam irradiation. Methods and Materials: Fift y-nine patients with T2b-T3c prostatic adenocarcinoma received 176 tra nsperineal ultrasound-guided conformal high-dose rate (HDR) boost impl ants. All patients received concomitant external beam pelvic irradiati on. Dose escalation of the three HDR-CB fractions proceeded as follows : 5.5 Gy (30 patients), 6 Gy (20 patients), and 6.5 Gy (9 patients). T he CB dose was prescribed to the prostate contour as outlined using an online biplanar transrectal ultrasound probe. The urethra, anterior r ectal wall, and prostate boundaries were identified individually and o utlined at 5 mm intervals from the base to the apex of the gland. The CB using real-tine ultrasound guidance with interactive online isodose distributions was performed on an outpatient basis. As needles were p laced into the prostate, corrections for prostate displacement were re corded and the isodose distributions were recalculated to represent th e new relationship between the needles, prostate, and normal structure s. No computerized tomography (CT) planning or implant preplanning was required. Results: No patient was rejected based on poor geometrical relation of pelvic structures. In every implant performed, prostate di splacement was noted. Craniocaudal motion of the gland ranged from 0.5 -2.0 cm (mean = 1.0 cm), whereas lateral displacement was 0.1-0.4 cm. With the interactive online planning system, organ motion was immediat ely detected, accounted for, and corrected prior to each HDR treatment , The rectal dose has ranged from 45 to 87%, and the urethral dose fro m 97 to 112% of the prostate dose. It is significant to note that oper ator dependence has been completely removed because the interactive on line planning system uniformly guides the physicians. Conclusions: Wit h ultrasound guidance and the interactive online dosimetry system, org an motion (as compared to external beam) is insignificant because it c an be corrected during the procedure without increasing target volume margins. Common pitfalls of brachytherapy, including operator dependen ce and difficulty with reproducibility, have been eliminated with the intraoperative online planning system.