A method for patient-specific absorbed dose estimation for internal beta emitters.

The purpose of the study was to determine a technique for estimating patient-specific absorbed radiation doses in radioimmunotherapy and other internal emitter therapies. Beta Radiation sources were considered, with 90Y being the radionuclide of primary interest. Organ uptake of activity was determined using a merged set of computed tomography and planar nuclear images. Estimation of local absorbed dose was accomplished using a voxel source kernel. Voxel size was 0.2 x 0.2 x 0.5 cm; dimensions were from the digital resolution of the nuclear and computed tomography data sets. Dose-volume histograms were also obtained due to the voxel nature of the estimations. Organ dose estimates were made for two patients receiving the chimeric anticarcinoembryonic antigen antibody cT84.66. Considerable variation was observed when comparing the voxel kernel results with medical internal radiation dosimetry values obtained via the MIRDOSE3 program. Primary uncertainty in the organ dose estimates was determined to be due to the variation in organ mass. By correcting the S values in that program by the organ mass ratio, we found generally good agreement between our method and MIRDOSE3. We conclude that patient-specific absorbed doses can be estimated for 90Y-labeled antibodies.