Purpose: Expected organ doses from the intra-hepatic-arterial (IHA) administration of 99mTc-macro-aggregated-albumin (MAA) for lung-shunt-fraction (LSF) estimation prior to 90Y-SIRT or radioembolization are now requested by the FDA for new 90Y-radioembolization trials. Unfortunately to date, no such values have been published. Traditionally, organ doses from any radionuclide administrations are estimated through MIRD-based dosimetry following a laborious prospective study to establish radiotracer biodistribution through serial imaging. Here, we instead relate the possible IHA 99mTc-MAA biodistributions, considering the worst-case LSF and 99mTc-MAA disassociation values, to the published biodistributions and organ doses following intravenous 99mTc-MAA and intravenous 99mTc-pertechnetate administrations to estimate organ doses following IHA 99mTc-MAA.
Methods: Three potential IHA 99mTc-MAA biodistributions were considered. Case1) all 99mTc-MAA is sequestered in the liver (0% LSF, 0% disassociation), and organ doses are estimated with OLINDA1.1 with a liver source organ of 99mTc-MAA (8.67MBq-h/MBq residence time). Case2) all 99mTc-MAA exits the liver into venous circulation (100% LSF, 0% disassociation), and organ doses follow intravenous 99mTc-MAA ICRP-80 values. Case3) all 99mTc-MAA disassociates and exits the liver into venous circulation (100% LSF, 100% disassociation), and organ doses follow intravenous 99mTc-pertechnetate ICRP-80 values. We report worst-possible individual organ doses (highest values across Cases) and the expected organ doses for typical LSF and disassociation (weighted linear combinations of Cases).
Results: The liver (98.6 mGy/GBq), lung (66.0 mGy/GBq), and colon (42.0 mGy/GBq) received the largest doses in Case1, Case2, and Case3, respectively. Following 0.185 GBq (5 mCi) IHA 99mTc-MAA, the liver and lung doses were 18.2 and 12.2 mGy (worst-case), 15.8 and 2.3 mGy (typical 10% LSF, nominal 5% disassociation), and 11.7 and 3.3 mGy (high 20% LSF, high 20% disassociation).
Conclusion: Our novel approach uses published intravenous 99mTc-MAA and 99mTc-pertechnetate dosimetry in conjunction with OLINDA1.1 liver dosimetry to provide previously unknown and unpublished worst-case and typical-case organ doses following IHA 99mTc-MAA.