Biodistribution and dosimetry of free118Te, anin vivogenerator of the positron emitter118Sb for long-term positron emission tomography.

Abstract

Objective. Tellurium-118 (¹¹⁸Te;t_1/2= 6.00 ± 0.02 d) can act as anin vivogenerator of the positron emitter antimony-118 (¹¹⁸Sb;t_1/2= 3.6 ± 0.3 min), enabling positron emission tomography (PET) over a week or longer. This work assessed absorbed doses associated with free¹¹⁸Te to establish a dosimetric safety basis for¹¹⁸Te radiopharmaceuticals.Approach. Injection solutions of free¹¹⁸Te were prepared by alpha-particle irradiation of an enriched tin-116 target followed by radiochemical isolation.Ex vivobiodistribution in healthy female Slc:ICR mice was acquired at seven time points from 2 h to 29 d postinjection (n= 6 per time point). Time-integrated activity coefficients were computed from the biodistribution profiles and extrapolated to a human model using relative mass scaling. Absorbed dose coefficients (ADCs) were calculated following the Medical Internal Radiation Dose formalism with computational phantoms implemented in the dosimetry software OLINDA. Dosimetric contributions from¹¹⁸Te and its coproduced radioisotopic impurity^119mTe (t_1/2= 4.69 ± 0.04 d), along with their equilibrium daughters¹¹⁸Sb and¹¹⁹Sb, were individually assessed.Main results. The kidneys exhibited the highest ADC in both mouse (2666.0 mGy MBq^-1) and human (2.639 mGy MBq^-1) models. Bone received the second-highest ADC in the mouse model, 1855.5 mGy MBq^-1. Antimony-118 dominated absorbed doses across all organs examined, accounting for more than 82% of ADCs in both models. Contributions from¹¹⁸Te,^119mTe, and¹¹⁹Sb were minor by comparison.Significance. The kidneys and bone were identified as the primary dosimetric targets of free¹¹⁸Te, with its daughter¹¹⁸Sb being the principal dose contributor. The limited dosimetric impact from¹¹⁸Te provides justification for its use as anin vivogenerator of¹¹⁸Sb for long-term PET. The ADCs reported here offer a quantitative basis for assessing the dosimetric safety of¹¹⁸Te radiopharmaceuticals.