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 ^99mTc-macroaggregated-albumin (IHA ^99mTc-MAA) routinely used in ⁹⁰Y-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 ^99mTc-MAA that incorporates three in vivo constituent biodistributions, the ^99mTc-MAA that escape the liver due to LSF, and the ^99mTc-MAA dissociation fraction (DF). Methods: The potential in vivo biodistributions for IHA ^99mTc-MAA are: Liver-Only MAA with all activity sequestered in the liver (LSF = 0&DF = 0), Intravenous MAA with all activity transferred intravenously as ^99mTc-MAA (LSF = 1&DF = 0), and Intravenous Pertechnetate with all activity is transferred intravenously as ^99mTc-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 ^99mTc-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 <27 and <32 mGy/GBq. For Intravenous MAA, the lung as source organ received the highest dose at 66 and 97 mGy/GBq; all remaining organs received <16 and <21 mGy/GBq. The organ with the highest dose for 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) ^99mTc-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 ^99mTc-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 ^99mTc-MAA.