Computer-aided geometric reconstruction of Fletcher-Suit source positions.

A computer-aided method for reconstruction of the source positions of a Fletcher-Suit applicator has been developed. The tandem source positions are determined by digitizing of the tip and two arbitrary points on the shaft from each of two orthogonal simulator films. A colpostat source position is reconstructed by digitizing of a single point on the endcap and three arbitrary points on the cylindrical sidewalls of the colpostat on the films. This computer-aided method considers the true projection geometry and applicator shape and permits localization of the source positions to within a mean error of less than 1 mm. Compared with the conventional method, the new approach (1) is more time efficient because only a few easily identified points are digitized, (2) allows localization when the tandem sources are shifted by a spacer or when colpostat sources are difficult to visualize on the lateral film, and (3) is more accurate than the conventional technique because no manual drawing of source positions on films is involved.