An application of equivalent TAR method to fast reconstructor of three dimensional dose distribution

We modify Equivalent TAR method by means of alternating parameters and equations on the basis of the theory, in order to realize targets of following items. (1) Arbitrary plane of calculation such as plane perpendicular to the beam axis, coronal plane, sagittal plane, can be selected. (2) Irregular shaped field can be applied. (3) Calculation speed must be fast enough to be used in clinical routine work, and application for conformation radiotherapy must be possible. A method of speed up is replacing weighting factor Wijk to exponential function so as to be calculated easily and rapidly. Another method of shortening calculation time was employment of fast reconstructor of dose distribution implemented in treatment planning computer system THERAC-2300. One several tenth calculation time of averaged level minicomputer was realized. About few ten seconds per portal is our final target. Our newly developed software is for multi-portal fixed irradiation involving technique of irregular shaped field and wedge filters. CT images up to 12 slices together are able to be entered and to be employed in one case of dose distribution planning. In case CT slice is not available, our software can accept contours of body outline and inhomogeneity. Positioning function for beam alignment on CT images with dose distribution curve employing 3 points mark is available by the dedicated software. Also entry of three dimensional target volume on each CT image is possible by the software. (J.P.N.)