IRRADIATION OF LOCALIZED PROSTATIC-CARCINOMA WITH A COMBINATION OF HIGH-DOSE-RATE IR-192 BRACHYTHERAPY AND EXTERNAL-BEAM RADIOTHERAPY WITH 3 TARGET DEFINITIONS AND DOSE LEVELS INSIDE THE PROSTATE-GLAND

Purpose: Localized prostate cancer was treated with combined external beam radiotherapy and high dose rate Ir-192 brachytherapy with the pur pose of a high dose, The technical aspects of a modified treatment are described. Methods: The brachytherapy was given in two sessions prece ded and succeeded by external beam radiation. The radioactive source w as temporarily implanted by a remote afterloading device through six t o 15 needles inserted transperineally guided by transrectal ultrasound . The entire prostate gland was included in the clinical target volume . The urethra and the tumour volume could be defined and irradiated to different dose levels in more than 90% of the patients. Results: Fift y-four patients were treated. The total dose to the prostate was appro ximately 70 Gy and to the tumour volume 80 Gy. By calculating the corr esponding dose given by 2.0 Gy fractions, considering the radiobiology by using the LQ formula and assuming an alpha/beta value for prostate tissue of 10, the dose to the prostate was approximately 84 Gy and to the tumour volume 112 Gy. For the late effects to the urethra an alph a/beta value of 3 was used, which corresponds to 85 Gy, The brachyther apy could be given with accuracy except when the dorsal border of the prostate was concave. The dose distribution then tended to be less sat isfactory. Post-treatment calculations showed that the maximum dose to the rectum was 67 Gy (radiobiologically corrected to 88 Gy), given in a small volume. The early side effects from the brachytherapy were mi nimal. The treatment could not be performed as intended in four patien ts; three patients had a narrow pelvis and in one patient the prostate was unusually resilient, preventing the needles from being positioned properly. Conclusions: This modification of a previously reported bra chytherapy technique for prostate carcinoma permits a high radiation d ose to the tumour and to the prostate gland, which ultimately may impr ove local control. (C) 1997 Elsevier Science ireland Ltd.