NEUTRON DOSIMETRY IN IN VIVO MEASUREMENT OF INTRATHYROIDAL IODINE IN MAN BY ACTIVATION ANALYSIS

A collimated beam of neutrons from a reactor was used to irradiate the thyroid, inducing l28I which can be detected by external counting. Neutron dosimetry studies have been carried out with the unmodified beam and also using a boron filter to absorb incident thermal neutrons. Five methods were used to provide dose estimates and the results were in reasonable agreement, giving for a clinical examination at 20 kw reactor power a mean dose-equivalent and standard error of 20.4 ± 1.1 rem for the filtered beam, and 24.1 ± 1.2 rem for the unmodified beam due to neutrons at the thyroid. The concurrent γ-ray dose is 2.1 ± 0.2 rem. The dose to the eyes and gonads is less than 1% of the thyroid dose.