Evaluation of the reconstruction of brachytherapy implants in three-dimensions from stereo radiographs

The precision and the accuracy of the stereo-shift method for reconstruction of brachytherapy implants were evaluated. Analysis of shift films was performed by measuring the coordinates of the seeds in an experimental set-up in the laboratory, by manually calculating the coordinates of the seeds from the projection distances on the stereo-shift radiographs, and by using a computer-aided treatment planning system. The resultant reconstructed coordinates agreed well with each other. The uncertainties in precision for the coordinates were expressed as the standard deviation of the measurements. The standard deviation of the computer and manual measurements agreed well with predicted values by an analysis of the random uncertainties in the reconstruction parameters. The uncertainties were within 0.2 mm for the coordinates parallel to the plan of the film and were within 0.4 mm for the coordinate perpendicular to the plane of the shift film. The uncertainties in the accuracy of the reconstruction were compared with the values obtained in clinical practice as well as with the values reported in the literature. Suggestions are made to improve the accuracy.