Autoradiography-based, three-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 quantitative ¹²⁵I autoradiography. For the absorbed dose-rate calculation, we assume the activity from both ¹³¹I- and ⁹⁰Y-labeled radiopharmaceuticals would be distributed as is measured with the ¹²⁵I label. Two example cases are presented: an ovarian-carcinoma xenograft with an IgG 2ak monoclonal antibody and a neuroblastoma xenograft with meta-iodobenzylguanidine (MIBG). Considering all the volume elements in a tumor, we show, by comparison of histograms and also relative standard deviations, that the measured ¹²⁵I activity and the calculated ¹³¹I dose-rate distributions, are similarly non-uniform and that they are more non-uniform than the calculated ⁹⁰Y dose-rate distribution. However, the maximum-to-minimum ratio, another measure of non-uniformity, decreases by roughly an order of magnitude from one distribution to the next in the order given above.