Calculation of annual limits of intake of radionuclides by workers: significance of breast as an explicitly represented tissue.

Abstract

Specific absorbed fractions (SAFs) given herein provide data useful for calculating radiation doses from internally deposited radionuclides to the breasts, an organ important because of its radiosensitivity. These data were generated using a mathematical phantom which has the dimensions and weight of a reference adult female and has a breast-tissue compartment. Dose to the breast is weighted heavily by the ICRP in its Publication 30 in determining annual limits of intake of radionuclides by workers (ALIs). The mathematical phantom used by the ICRP to estimate the amount of energy absorbed by various target organs from a source of photons in some organ of the body has the dimensions and weight of a reference adult male and does not have a defined breast-tissue compartment. Consequently, the ICRP used the "remaining tissue" compartment of the phantom to represent breast tissue for the purpose of calculating ALIs. Although the SAFs to the breast compartment of the adult female phantom and the SAFs to the remaining tissue compartments of the phantom used by the ICRP may differ greatly, use of these newer data should not change the ALIs by more than 20% if the SAFs for other target organs from the ICRP phantom are retained. The ALIs thus computed varied from 82 to 104% of the ALIs published by the ICRP. If SAFs from the smaller adult female phantom are used for all target organs, the ALIs varied from 62 to 95% of the ALIs published by the ICRP. These conclusions are based on test calculations with 37 nuclides which are primarily photon emitters; these tests should demonstrate maximal differences. Using metabolic models specifically designed for females and using a different weighting scheme for target organs in females (i.e. not an average for both sexes) could either enlarge or diminish the ALIs, but these effects were not investigated.