High-dose-rate afterloading and the LQ-model--evaluation of efficacy in cervix cancer therapy

For short-time afterloading with high dose rates at irradiation treatment of gynecological tumors an adequate fractioning with reduced total dose is necessary considering the basically changed dose-time relation opposite to the common long-time brachytherapy. In addition to the careful clinical control of empiric found fractioning regimes for the primary and postoperative intrauterine and intravaginal afterloading therapy in cervix carcinoma and endometrium carcinoma, at which the surroundings reactions of the urine bladder, rectum and sheath, and also the tumor regression and relapses were investigated, a calculation of equivalent doses seems to be recommendable by means of mathematically formulated model conception according to the NSD formula and the LQ model. Changed exponents p for the fractioning rate N depending on the total treatments time were used for the rate calculations at slowly fractionated small-volume irradiation opposite to a higher fractionated percutaneous great-volume irradiation NSD conception was developed for. In LQ-model calculation changed coefficients mu for the repair half-life-time T in connection to the changed repair capacity in small volume brachytherapy were used. Knowing the compatibility and tumor efficiency of the rate-values and the alpha/beta-ratio for different fraction regimes were calculated and compared concerning their radiobiological equivalence and practical use. The calculations show a good clinical correspondence for single and total dosage in fractionated high dose rate afterloading of gynecological tumors.