Abstract
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Objectives Selective radio-embolization via the hepatic arteries of liver tumours using 90Y-resin beads (SirSpheres) is now an established therapy, however, A-V shunting of the spheres from the liver to the lungs is a dose-limiting factor. The aim of this work was to evaluate the dose deposited in the lungs in a pre-therapy scan using 99mTc labelled microspheres (MAA) prior to the therapeutic procedure.
Methods A validated method for CT-based quantitative SPECT (qSPECT) and an alternative planar geometric mean (GM) approach were compared. After injection of [99mTc]-MAA via the hepatic artery, a SPECT/CT was acquired and liver and lung uptake calculated using CT-based attenuation and scatter correction. After this scan, a calibrated systemic injection of [99mTc]-MAA was administered via a peripheral vein to quantify lung trapping of the microspheres in planar images by comparing pre- and post-injection GM count rates from regions defined for the lungs. The change in count rate can then be attributed to the known amount of radioactiviuty injected and, hence, the intial count rate can be quantified in terms of total MBq in the lungs from the dose given to the liver.
Results In an example study, qSPECT correctly accounted for all injected activity and found 80% of the dose was retained in the liver and 4% in the lungs. The planar method estimated ~4% of the dose in the lungs.
Conclusions The qSPECT method allows accurate calculation of organ-specific uptake, including the possibility of calculating the individual's therapeutic dose to the liver.The planar approach, on the other hand, offers a simplified method to quantify lung uptake alone.
- © 2009 by Society of Nuclear Medicine