Uncertainties on the committed equivalent dose to the thyroid as a function of age for different iodine isotopes

This study compares uncertainties of equivalent doses after internal contamination by 125I, 129I or 131I. Uncertainties were calculated using reported distributions of physiological parameters and Monte Carlo simulation. In adults, uncertainties increase from 131I to 125I and 129I with 1% of the population receiving 3.9, 4.0 and 7.2 times the median dose for the respective isotopes. In newborns, these values were 7.5, 12.3 and 19.0 for 131I, 125I and 129I respectively. The ratio of the beta dose delivered to the epithelium versus a homogeneous distributed dose was estimated for different iodine concentrations in colloid, epithelium and interstitium. In adults, for 131I, about 40% of the beta dose was delivered to the epithelial cells, whereas this fraction varied depending on the concentration for 125I and 129I, i.e. 20-30% at a relative epithelial concentration of 20% and 7-14% at a concentration of 3%. Small variations were observed depending on age.