Objective: The use of Y-90 microspheres to treat metastatic liver cancer is becoming widely utilized. Despite the fact that the microspheres are delivered directly to the liver, some activity may bypass the liver capillaries and be shunted to the lungs. To evaluate the percentage of pulmonary breakthrough, a pre-therapy test is performed using Tc-99m labeled spheres. The aim of this project was to compare two quantitative methods for assessing lung uptake, and consider the possibility of organ specific quantification.

Method: A previously validated method for achieving CT-based quantitative SPECT (1) was compared to a simple planar approach. A 44 year old man suffering from metastatic liver sarcoma was referred to the clinic for pre-therapy evaluation. After injection of Tc-99m labeled microspheres and routine imaging, a SPECT/CT was acquired and specific organ uptake values calculated. A further calibrated injection of [Tc-99m]-MAA was then given as a simplified alternative to quantify lung uptake by comparing pre and post counts.

Results: The quantitative SPECT/CT method 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 found ~4% of the dose in the lungs.

Conclusion: The quantitative technique we have developed allows for accurate calculation of organ specific uptake, which has important implications for treatment. The additional MAA injection offers a simplified but accurate method to quantify lung uptake.

(1) K Willowson, DL Bailey and C Baldock (2008) Quantitative SPECT reconstructions using CT-derived corrections Phys Med Biol 53:3099-3112