Quantitative SPECT and planar 32P bremsstrahlung imaging for dosimetry purpose –An experimental phantom study

Background: In this study, Quantitative 32P bremsstrahlung planar and SPECT imaging and consequent dose assessment were carried out as a comprehensive phantom study to define an appropriate method for accurate Dosimetry in clinical practice. Materials and Methods: CT, planar and SPECT bremsstrahlung images of Jaszczak phantom containing a known activity of 32P were acquired. In addition, Phantom contour was determined for attenuation correction and image registration. Reconstructed SPECT slices were corrected for attenuation effect using two different methods: conventional Chang`s method and an expectation maximization algorithm followed by CT and SPECT image registration. Cumulated activity was calculated by a predefined calibration factor. Both attenuation correction algorithms were quantitatively assessed by the Monte Carlo SIMIND program. Acquired planar Bremsstrahlung images were quantified by the Conjugate View Method, as well. Results: Calculated activities were statistically different among various quantification methods (P= 0.0001). When iterative expectation maximization algorithm and applied methods were used, mean calculated activity had the least difference with real activity of ±3%. Conclusion: Quantitative 32P Bremsstrahlung SPECT imaging could accurately determine administered activity and assess radiation dose if precise attenuation correction and appropriate registration with CT were done even without sophisticated scatter correction or when SPECT/CT machines are not available. Therefore, it has the potential of specific tumor/organ dosimetry in clinical practice. The best method for calculating activity is quantitative SPECT using iterative expectation maximization algorithm. Additionally, applied method for determining phantom contour was practical for attenuation correction and image registration.