Radiation Protection Dosimetry Advance Access originally published online on March 8, 2005
Radiation Protection Dosimetry 2005 113(3):290-299; doi:10.1093/rpd/nch464
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Estimation of the dose to the nursing infant due to direct irradiation from activity present in maternal organs and tissues
1 Institute of Radiation Protection and Dosimetry, Av. Salvador Allende s/n, Recreio, Rio de Janeiro, CEP 22780-160, Brazil
2 Federal Office for Radiation Protection, Department of Radiation Protection and Health, D-85762 Oberschleissheim, Germany
* Corresponding author: john{at}ird.gov.br
Received August 27, 2004, amended December 15, 2004, accepted January 27, 2005
Radionuclides deposited internally in the mother will give rise to a radiation dose in the infant in two ways. The radionuclides may be transferred through milk and give rise to an internal dose in the infant, or the radionuclides may emit photons that are absorbed by the infant, giving rise to an external dose. In this paper, the external dose to the newborn infant caused by direct irradiation was estimated for monoenergetic photons. Voxel models (also called voxel phantoms) of the mother and infant were made in three geometries. These models, consisting of volume elements, or voxels, were designed so that the infant model was placed in the lap, at the breast and on the shoulder of the mother model. The Visual Monte Carlo (VMC) code was used to transport the photons through the voxel models. Source regions for the emitted photons, such as the whole body, the thyroid, the lung, the liver and the skeleton, were chosen. For the validation of the calculation procedure, VMC results were favourably compared with the results obtained by using other Monte Carlo programs and also with the previously published results for specific absorbed fractions. This paper provides estimates of the external dose per photon to the infant for photon energies between 0.05 and 2.5 MeV. The external dose per photon estimates were made for the three geometries and for the sources listed above. The results show that, for the geometry of the nursing infant model at the breast, the highest dose to the infant per photon comes from radionuclides deposited in the mother's liver. For the nursing infant model at the shoulder, the highest dose to the infant per photon comes from radionuclides deposited in the mother's thyroid, and for the nursing infant model in the lap, the highest dose to the infant per photon comes from radionuclides deposited uniformly in the whole body. The dose per photon results were then used to estimate the dose an infant might receive over the lactation period (6 months) due to the incorporation of 1 Bq of a radionuclide by the mother. This information may be used to provide external dose estimates to the infant in the case of a known or suspected radionuclide incorporation by the mother due to, for example, a nuclear medicine procedure.
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