Abstract
Abstract
Objective
. Tellurium-118 (
118
Te;
t
1/2
= 6.00 ± 0.02 d) can act as an
in vivo
generator of the positron emitter antimony-118 (
118
Sb;
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 free
118
Te to establish a dosimetric safety basis for
118
Te radiopharmaceuticals.
Approach
. Injection solutions of free
118
Te were prepared by alpha-particle irradiation of an enriched tin-116 target followed by radiochemical isolation.
Ex vivo
biodistribution 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 from
118
Te and its coproduced radioisotopic impurity
119m
Te (
t
1/2
= 4.69 ± 0.04 d), along with their equilibrium daughters
118
Sb and
119
Sb, 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 from
118
Te,
119m
Te, and
119
Sb were minor by comparison.
Significance
. The kidneys and bone were identified as the primary dosimetric targets of free
118
Te, with its daughter
118
Sb being the principal dose contributor. The limited dosimetric impact from
118
Te provides justification for its use as an
in vivo
generator of
118
Sb for long-term PET. The ADCs reported here offer a quantitative basis for assessing the dosimetric safety of
118
Te radiopharmaceuticals.