AUTORADIOGRAPHY-BASED, 3-DIMENSIONAL CALCULATION OF DOSE-RATE FOR MURINE, HUMAN-TUMOR XENOGRAFTS

A Fast Fourier Transform method for calculating the three-dimensional dose rate distribution for murine, human-tumor xenografts is outlined. The required input includes evenly-spaced activity slices which span the tumor. Numerical values in these slices are determined by quantita tive I-125 autoradiography. For the absorbed dose-rate calculation, we assume the activity from both I-131- and Y-90-labeled radiopharmaceut icals would be distributed as is measured with the I-125 label. Two ex ample cases are presented: an ovarian-carcinoma xenograft with an IgG 2ak monoclonal antibody and a neuroblastoma xenograft with meta-iodobe nzylguanidine (MIBG). Considering all the volume elements in a tumor, we show, by comparison of histograms and also relative standard deviat ions, that the measured I-125 activity and the calculated I-131 dose-r ate distributions, are similarly non-uniform and that they are more no n-uniform than the calculated Y-90 dose-rate distribution. However, th e maximum-to-minimum ratio, another measure of non-uniformity, decreas es by roughly an order of magnitude from one distribution to the next in the order given above.