The aim of this study was to examine the agreement of pretreatment 99mTc-macroaggregated albumin imaging performed for selective internal radiation therapy (SIRT) workup with 90Y percentage lung shunt (PLS) and regional hepatic distribution in subsequent post-therapy bremsstrahlung imaging.Patients and methods
Planar images were used to calculate PLS. The significant 90Y bremsstrahlung scatter required background correction. Results using both 90Y lung background regions of interest (ROI) reported in previous studies and extended ROIs (reflecting lung background variation) were compared with 99mTc-MAA PLS. Lesion and healthy liver volumes were outlined on diagnostic computed tomography scans and registered to 99mTc-MAA and 90Y single-photon emission computed tomography/computed tomographydata. Single-photon emission computed tomography voxel values were normalized to injected 90Y activity. Volume mean activities were calculated, and converted into the mean absorbed dose. Agreement was quantified using Bland–Altman analysis.Results
PLS: The bias using previous studies’ lung background ROIs was −10.71%, with a 95% confidence interval (CI) of −18.79 to −2.64%. The extended ROI yielded a bias of 0.77% (95% CI: −2.23 to 3.70%). Liver: The healthy liver bias was 0.01 MBq/ml (0.17 Gy), with a −0.05 to 0.06 MBq/ml (95% CI:0.80 –1.93 Gy). The lesion mean activity/ml bias was −0.02 MBq/ml (3.71 Gy), with a −0.81 to 0.76 MBq/ml (95% CI: −35.49 to 28.07 Gy).Conclusions
The PLS agreement was sensitive to the 90Y lung background correction ROI, potentially explaining a previously published controversy. The mean activity and absorbed dose agreement for the metastatic lesions was poorer than the healthy liver volumes studied here.