PATIENT-SPECIFIC DOSIMETRY USING QUANTITATIVE SPECT IMAGING AND 3-DIMENSIONAL DISCRETE FOURIER-TRANSFORM CONVOLUTION

he objective of this study was to develop a three-dimensional discrete Fourier transform (3D-DFT) convolution method to perform the dosimetr y for I-131-labeled antibodies in soft tissues. Methods: Mathematical and physical phantoms were used to compare 3D-DFT with Monte Carlo tra nsport (MCT) calculations based on the EGS4 code. The mathematical and physical phantoms consisted of a sphere and a cylinder, respectively, containing uniform and nonuniform activity distributions. Quantitativ e SPECT reconstruction was carried out using the circular harmonic tra nsform (CHT) algorithm. Results: The radial dose profile obtained from MCT calculations and the 3D-DFT convolution method for the mathematic al phantom were in close agreement The root mean square error (RMSE) f or the two methods was <0.1%, with a maximum difference <21%, Results obtained for the physical phantom gave a RMSE <0.1% and a maximum diff erence of <13%; isodose contours were in good agreement SPECT data for two patients who had undergone I-131 radioimmunotherapy (RIT) were us ed to compare absorbed-dose rates and isodose rate contours with the t wo methods of calculation. This yielded a RMSE <0.02% and a maximum di fference of <13%, Conclusion: Our results showed that the 3D-DFT convo lution method compared well with MCT calculations. The 3D-DFT approach is computationally much more efficient and, hence, the method of choi ce. This method is patient-specific and applicable to the dosimetry of soft-tissue tumors and normal organs, It can be implemented on person al computers.