Clinical application of high dose rate interstitial radiation therapy

: High dose rate interstitial radiation (HDR-ISRT) with afterloading method is newly introduced radiotherapeutic modality which can be performed in short time and can lower the radiation exposure to the medical personnel. Afterloading Buchler IR was used in this study which obtains dose distribution by continuous oscillation of small high intensity iridium-192 source in 2.2 mm diameter applicator. The dose calculation programme for HDR-ISRT developed by us proved to be satisfactorily reliable except in the close proximity of less than 5 mm from the applicator. By using the developed programme, optimal applicator insertion interval was calculated which attain the dose homogeneity of 11% in a given plane. It was shown that this oscillating iridium source can give satisfactory dose distribution even if the applicators are inserted with interval greater than 1.5 cm. The clinical application of the HDR-ISRT with evaluable lesions has been performed in 23 sites in 21 patients. In 13 sites local control was obtained in spite of the advanced stage of the tumors. Radiation injury was shown in 5 sites, of which 3 needed to be treated surgically. The analysis of 23 sites which underwent HDR-ISRT showed that external radiation less than 50 Gy, HDR-ISRT dose between 15 to 20 Gy and total dose between 60 to 70 Gy in 40 to 100 days seemed necessary to obtain local control without radiation injury.