A SIMPLE METHOD OF DOSAGE CALCULATION IN ROTATION THERAPY

Abstract

In case of rotation therapy, the first step for the estimation of central axis dose is to obtain the tumor skin distance every 10-20 degrees around the patient contour. Then tissue-air ratio corresponding to each distance can be read from the ready-made T.A.R. table. These are summed and averaged. In practice, however, the method is somewhat tedious and timeconsuming, which is a disadvantage in busy department. In this paper, a rapid and simple method to obtain the average tumor-skin distance in case of rotation therapy of the patient with carcinoma of uterine cervix was described. 50 samples were randomly drawn from the group of carcinoma of uterine cervix that has been recieving radiation therapy in our department. Their contour, antero-posterior and lateral dimensions were statisfying analysed. From this analysis the following conclusion was obtained. If the anteroposterior and lateral dimensions of the patient were measured, the average skin-tumor distance could be calculated from the graph (Fig. 4) based on the equation that was statisfying obtained from 50 patients. The differences of dosage calculation between the method of averaged T.A.R. and this simple method were 2% at the most.