According to the remarkable progress of high energy medical radiation apparatuses, the part of the teletherapyusing linear accelerator and telecobait is now occupying almost the whole portion of cancer therapy in the fieldof radiation treatment. However, even in the present days, inserting sealed small source theraphy appliedinterstitially and intracavitary shows better results in some kinds of tumors just as the tumors of the tongue andthose of the uterine cervix, especially, high dose rate sources are more effective for it. On the technic of theseinserting therapy, the dose calculations in the tumor ar the most troublesome procedures to determine the therapytechnic, and its technic must be doing under accurate dose distribution, dosimetry and localization. The high doserate remotely controlled afterloading apparatus, Toshiba RAL 303, was installed in Yonsei Cancer Center in 1979.We applicated the computer technique to the dose computation and enabled to improve the accuracy of intracavitaryirradiation for the cervix cancer. To obtaine the exact localization of applications in the uterine cercix. Wefabricated the simulating scaler and metallic o-ring contacting in tandem. Optimum standard arrangements ofradiation sources were confiremd as 10 types, according to statistical evaluation of patients who had receivedbranchtherapy.