A simple method for projecting isodose charts of linear radium sources on planes oblique to the longitudinal axis.

Abstract

This method of graphic projection of isodose curves for linear radium sources was devised to enable isodose charts to be used for the determination of two orthogonal films of a radium applicator. The commonest use for these charts is dosage calculation in radium therapy of cancer of the cervix uteri according to the method described by Fletcher, Wall, Bloedorn, Shalek and Wootton (1953). A contour of the pelvic brim with the position of the radium sources in the tandem and in the ovoids is traced on transparent paper on the antero-posterior film. Isodose charts of the three components of the radium applicator are then placed under the contour, superimposed on one another, on an illuminator. In most cases, however, the longitudinal axis of the tandem lies on a plane oblique to the frontal plane of the pelvis (Fig. 1). Therefore, the angle of the tandem to the frontal plane should be first measured on the lateral film and then the appropriate chart should be applied to the tandem as seen in the antero-poste...