Patient-specific dosimetry using quantitative SPECT imaging and three-dimensional discrete Fourier transform convolution.
The objective of this study was to develop a three-dimensional discrete Fourier transform (3D-DFT) convolution method to perform the dosimetry for 131I-labeled antibodies in soft tissues.


METHODS
Mathematical and physical phantoms were used to compare 3D-DFT with Monte Carlo transport (MCT) calculations based on the EGS4 code. The mathematical and physical phantoms consisted of a sphere and a cylinder, respectively, containing uniform and non-uniform activity distributions. Quantitative SPECT reconstruction was carried out using the circular harmonic transform (CHT) algorithm.


RESULTS
The radial dose profile obtained from MCT calculations and the 3D-DFT convolution method for the mathematical phantom were in close agreement. The root mean square error (RMSE) for 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 difference of < 13%; isodose contours were in good agreement. SPECT data for two patients who had undergone 131I radioimmunotherapy (RIT) were used to compare absorbed-dose rates and isodose rate contours with the two methods of calculation. This yielded a RMSE < 0.02% and a maximum difference of < 13%.


CONCLUSIONS
Our results showed that the 3D-DFT convolution method compared well with MCT calculations. The 3D-DFT approach is computationally much more efficient and, hence, the method of choice. This method is patient-specific and applicable to the dosimetry of soft-tissue tumors and normal organs. It can be implemented on personal computers.
Akabani
G
G
Department of Radiation Oncology, University of Nebraska Medical Center, Omaha 68198-1045, USA.
Hawkins
W G
WG
Eckblade
M B
MB
Leichner
P K
PK
D000465:Algorithms; D005583:Fourier Analysis; D006801:Humans; D007457:Iodine Radioisotopes; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D016719:Radioimmunodetection; D016499:Radioimmunotherapy; D011880:Radiotherapy Planning, Computer-Assisted; D015899:Tomography, Emission-Computed, Single-Photon
D007457:Iodine Radioisotopes