Feasibility study combining low dose rate Ir-192 brachytherapy and external beam radiotherapy aiming at delivering 80-85 Gy to prostatic adenocarcinoma

Background: Increasing the radiation dose to prostatic adenocarcinoma has p rovided higher local control rates. A total of 80 Gy seem necessary to achi eve this goal but patient set-up and prostate motion remain difficult probl ems to solve in conformal radiotherapy. Brachytherapy which overcomes these points could be an alternative way to external beam boost fields. We wante d to transpose the irradiation models largely used in cervix cancer treatme nt combining external beam radiotherapy and low dose rate brachytherapy. Materials and methods: In 71 patients with 19.5 and 13 ng/ml mean and media n PSA levels, respectively, a dose escalation from 74 to 85 Gy was performe d in four groups. Results: Shifting from intraoperative placement of sources vectors (Group I ) to positioning under ultrasound controls (groups II-IV), improving the im plantation shape and optimizing radiation delivery to urethral bed have red uced the total dose to rectal wail under 65 Gy and to urethra under 100 Gy. Rectal/prostate dose ratio was lowered from 0.7 (Groups I-II) to 0.58 (Gro ups III-IV) while avoiding problems resulting from pelvic bone arch interfe rence, prostate volume or seminal vesicles location. The mean and median fo llow-up periods are 28 and 18 months. In Groups III and IV 85% of patients without hormonotherapy treated with 80-85 Gy normalized PSA under 1 ng/ml w ithin 6 months. No severe late effect has been noted for patients implanted under echographic control. Conclusions: The method described allows to deliver 85 Gy. Longer follow-up is however needed but the levels of dose delivered are not expected to ind uce prohibitive side effects. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.