Organ-level internal dosimetry for intra-hepatic-arterial administration of 99mTc-macroaggregated albumin

Purpose There are no published data on organ doses following intra-hepatic-arterial administration of Tc-99m-macroaggregated-albumin (IHA Tc-99m-MAA) routinely used in Y-90-radioembolization treatment planning to assess intra- and extra-hepatic depositions and calculate lung-shunt-fraction (LSF). We propose a method to model the organ doses following IHA Tc-99m-MAA that incorporates three in vivo constituent biodistributions, the Tc-99m-MAA that escape the liver due to LSF, and the Tc-99m-MAA dissociation fraction (DF). Methods The potential in vivo biodistributions for IHA Tc-99m-MAA are: Liver-Only MAA with all activity sequestered in the liver (LSF = 0&DF = 0), Intravenous MAA with all activity transferred intravenously as Tc-99m-MAA (LSF = 1&DF = 0), and Intravenous Pertechnetate with all activity is transferred intravenously as Tc-99m-pertechnetate (LSF = 0&DF = 1). Organ doses for Liver-Only MAA were determined using OLINDA/EXM 2.2, where liver was modeled as the source organ containing Tc-99m-MAA, while those for Intravenous MAA and Intravenous Pertechnetate were from ICRP 128. Organ doses for the general case can be determined as a weighted-linear-combination of the three constituent biodistributions depending on the LSF and DF. The maximum-dose scenario was modeled by selecting the highest dose rate for each organ amongst the three constituent cases. Results For Liver-Only MAA, the liver as source organ received the highest dose at 98.6 and 126 mGy/GBq for the adult male and adult female phantoms, respectively; all remaining organs received Intravenous MAA, the lung as source organ received the highest dose at 66 and 97 mGy/GBq; all remaining organs received Intravenous Pertechnetate was the upper-large-intestinal wall at 56 and 73 mGy/GBq; all remaining organs received <26 and <34 mGy/GBq. The liver and lung doses for the maximum-dose scenario with 5 mCi (185 MBq) Tc-99m-MAA were estimated at 18.2 and 12.2 mGy, and 23.3 and 17.9 mGy, for the adult male and adult female phantoms, respectively. Conclusion Organ dose estimates following IHA Tc-99m-MAA based on constituent biodistribution models and patient-specific LSF and DF values have been derived. Liver and lung were the organs with highest dose, receiving at most 15-25 mGy in the maximum-dose scenario, following 5 mCi IHA Tc-99m-MAA.

Automated summary

This study proposes a method to model organ doses following intra-hepatic-arterial administration of Tc-99m-macroaggregated-albumin (IHA Tc-99m-MAA). The results show that the liver and lung receive the highest doses in the maximum-dose scenario.