Comparison Of 2d Planar Versus 3d Spect/Ct Lung Shunt Fraction Calculation From Tc-99m M A A Pre-Y-90 Imaging For Hepatic Microsphere Radioembolization.

601 Objectives: omparison of 2D planar versus 3D SPECT/CT lung shunt fraction calculation from 99mTc MAA pre-90Y imaging for hepatic microsphere radioembolization. Objectives: It has been previously reported in the literature that 2D imaging for pre-90Y 99mTc MAA imaging overestimates calculation of the lung shunt fraction (LSF). This can potentially bias the accurate estimation of the 90Y microsphere treatment dose. The objective of this study is to compare 99mTc MAA LSF from 2D planar imaging versus 3D from SPECT/CT and to examine its impact on 90Y dosimetric analysis for resin (RM) or glass (GM) hepatic microsphere radioembolization (MSRE). Methods: LSF from pre-90Y 99mTc MAA was obtained using two different methodologies in 21 patients (12 with hepatocellular carcinoma and 9 with liver mets) who were scheduled to receive 90Y treatment with either RM or GM. The first method is based on conventional gamma camera conjugate anterior-posterior imaging and geometric mean calculation, and, the second method is based on volumetric 3D calculation from functional/anatomical SPECT/CT images utilizing specialized segmentation and dosimetry software (PLANET, DOSIsoft, Inc., Miami, FL). Comparison with statistical analysis was performed on the calculation of LSF in 2D versus 3D. The difference in the predicted absorbed dose to the lungs from the prescribed 90Y dose, as calculated based on 2D versus 3D LSF was also obtained. Results: The comparison showed the LSF was overestimated in 2D versus 3D in 18/21 patients with a mean value of 45% [range 14% to 73%]. It was also observed that in a small sub-group of patients 3/21, who had very low LSF in 2D (mean 2.1%) the LSF could be actually overestimated in 3D. This sub-group presented in all 3 cases with a focal right hepatic lobe lesion very close to the diaphragm. The mean difference in absorbed dose to the lungs when calculated based on 2D versus 3D LSF was 17% [range in Gy was 0.04 to 9.24]. Conclusions: In the large majority of patients in our study group we verified that 2D planar imaging significantly overestimates LSF as compared to 3D from SPECT/CT imaging. In our study group, we observed that in patients with focal right lobe liver lesions near the diaphragm 3D analysis could slightly overestimate LSF as compared to 2D. Calculation of LSF in 3D from SPECT/CT imaging using appropriate segmentation and dosimetric analysis tools can be very useful in predictively planning the treatment dose in patients who would receive 90Y hepatic MSRE and potentially reducing the risk of increased radiation dose to the lungs.