Irradiation of localized prostatic carcinoma with a combination of high dose rate iridium-192 brachytherapy and external beam radiotherapy with three 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 purpose of a high dose, The technical aspects of a modified treatment are described. Methods: The brachytherapy was given in two sessions preceded and succeeded by external beam radiation. The radioactive source was temporarily implanted by a remote afterloading device through six to 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: Fifty-four patients were treated. The total dose to the prostate was approximately 70 Gy and to the tumour volume 80 Gy. By calculating the corresponding 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 alpha/beta value of 3 was used, which corresponds to 85 Gy, The brachytherapy could be given with accuracy except when the dorsal border of the prostate was concave. The dose distribution then tended to be less satisfactory. 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 minimal. The treatment could not be performed as intended in four patients; 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 brachytherapy technique for prostate carcinoma permits a high radiation dose to the tumour and to the prostate gland, which ultimately may improve local control. (C) 1997 Elsevier Science ireland Ltd.