DETERMINATION OF THE APPROPRIATE FRACTION NUMBER AND SIZE OF THE HDR BRACHYTHERAPY FOR CERVICAL-CANCER

Based on the linear-quadratic model, we have made two isoeffect tables for transforming the traditional low dose rate (LDR) point A doses at 20, 30, 40, 50, 60, and 70 Gy to those of the high dose rate (HDR) do se per fraction. HDR fractions ranged from 1 to 12, with corresponding sizes for each fraction. We also propose the therapeutic gain ratio ( TGR) method for determining the appropriate fraction number of HDR bra chytherapy in cervical cancer. TGR is defined as addition of the calcu lated biological therapeutic difference with the supposed physical the rapeutic difference of HDR brachytherapy. Through the TGR method, we p redicted that after 2 to 3, 2 to 4, and 4 to 7 fractions of HDR treatm ents, the tumor control rate and complication rate would be equivalent to those of LDR point A doses of 30, 40, and 70 Gy, respectively. The TGR is affected by many factors, such as the equivalent total dose of LDR, dose rate of LDR, KDR fraction number, T-1/2, and differences be tween LDR and HDR in the dose in critical organs. The TGR method might explain why a low fraction number of HDR can be used in clinical prac tice. We may use this principle to replace the traditional trial-and-e rror method for transcribing the relationship between LDR and HDR trea tments. (C) 1996 Academic Press, Inc.