To date, internal emitter therapy has been guided by dose calculations based on stylized phantoms representing average individuals, and results for the most part have not been clinically meaningful. Validation of theoretical calculations of absorbed fractions and absorbed doses is an element that has been needed for such calculations. We propose the use of state-of-the-art quantitative SPECT imaging advances combined with Monte Carlo source transport calculations to provide accurate estimates of absorbed radiation dose to replace those available from current internal dose models. We will implement planar and SPECT reconstruction methods that compensate for attenuation, scatter, septal penetration, spatial resolution, and partial-volume effects to obtain accurate planar projection and voxel estimates of the cumulative activity, using a combined SPECT/CT nuclear medicine camera that permits near simultaneous acquisition of anatomic and functional 3D data, with minimal registration problems. We will determine the accuracy of activity estimation from the quantitative methods and reconstruction algorithms, through comparison of measured activity values in simple and complex anthropomorphic phantoms to known values. We will convert activity to radiation dose in a voxel environment using well established Monte Carlo transport algorithms and compare the calculated doses to theoretical values, as well as values measured in phantoms and medium sized animals using implanted MOSFET minidosimeters. [unreadable] [unreadable]