PURPOSE: The purpose is to investigate the possibility of evaluate the lung shunt fraction LSF with SPECT image in planning with Tc-99m of hepatic HCC treatments with Y-90 microspheres, comparing the results with those obtained with planar images.
METHODS: Firstly, for a patient with a predictably high shunt, the 4 planar images are used as in the classic method to determine PLANAR LSF. Second, to determine the SPECT LSF, the SPECT images acquired for planning the therapeutic activity, and therefore centered in the hepatic region, are used. These images does not cover the entire lung but only some slices. Advantage is taken of the fact that the distribution of 99MTc in healthy lung tissue is homogeneous. Then the activity concentration in the lung can be known and the SPECT LSF can be calculated.
RESULTS: The values obtained for PLANAR LSF and SPECT LSF are 11% and 28%, respectively. The results for the lung dose Dlung are of 24.50 Gy and 7.92 Gy, respectively.
CONCLUSION: In this study, LSF and lung absorbed dose Dlung based in planar static and SPECT/CT images acquired with 99MTc, have been described and compared. The results show a dependence between the absorbed dose in the lung with the LSF according to a rational function f = LSF/(1-LSF). The values of LSF and Dlung obtained with planar method are 2.51 and 3.09 higher than the values obtained with SPECT method, respectively. This is attributed to the differences in the quantification method, especially to the absence of attenuation correction in the planar method. In the LSF values, the difference is direct, but in the case of the Dlung the difference is greater due to covariant dependence of dose with activity and LSF. Practically for the future, the SPECT-CT method is better and will be applied in new patients.