A computer-assisted rapid method for source localization in interstitial implants

A new technique was developed to avoid the difficulties encountered with conventional source localization techniques used in implant dosimetry. This improved method does not depend for precision on accurate positioning of the X-ray target and places no constraint upon the radiographic technique other than that the sources should project upon the film. In addition, this method does not require positive identification of the source images on the radiographs, but employs computer methods to select the proper source coordinates from three sets of randomly digitized image coordinates. The method utilizes a precision jig containing fiducial marks in two planes parallel to the X-ray film. From the projection of the fiducial marks on the film, the spatial coordinates of the X-ray target as well as the sources may be determined to a precision of within ¹/₂%. Because of the convenience and quality of radiographs, a double stereo-shift method which results in three radiographs is preferred. By means of computer techniques it is possible to search for intersections between the computed X-ray target points and the image coordinates. Any ambiguities which may arise from the first set of stereo films are removed by comparison with the second set of stereo films. This method is considerably more precise than conventional techniques and is also easier to use. Because positive identification of each seed image is no longer required, the digitization of image coordinates is extremely rapid which is a welcome time-saving device. The method is also capable of being extended to automatic scanning techniques which would eliminate the manual digitization of image coordinates.