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

Objective. Tellurium-118 (118Te;t1/2= 6.00 ± 0.02 d) can act as anin vivogenerator of the positron emitter antimony-118 (118Sb;t1/2= 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 impurity119mTe (t1/2= 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.