title: Foetal dose conversion coefficients for ICRP-compliant pregnant models from idealised proton exposures.
abstract: Protection of pregnant women and their foetus against external proton irradiations poses a unique challenge. Assessment of foetal dose due to external protons in galactic cosmic rays and as secondaries generated in aircraft walls is especially important during high-altitude flights. This paper reports a set of fluence to absorbed dose conversion coefficients for the foetus and its brain for external monoenergetic proton beams of six standard configurations (the antero-posterior, the postero-anterior, the right lateral, the left lateral, the rotational and the isotropic). The pregnant female anatomical definitions at each of the three gestational periods (3, 6 and 9 months) are based on newly developed RPI-P series of models whose organ masses were matched within 1% with the International Commission on Radiological Protection reference values. Proton interactions and the transport of secondary particles were carefully simulated using the Monte Carlo N-Particle eXtended code (MCNPX) and the phantoms consisting of several million voxels at 3 mm resolution. When choosing the physics models in the MCNPX, it was found that the advanced Cascade-Exciton intranuclear cascade model showed a maximum of 9% foetal dose increase compared with the default model combination at intermediate energies below 5 GeV. Foetal dose results from this study are tabulated and compared with previously published data that were based on simplified anatomy. The comparison showed a strong dependence upon the source geometry, energy and gestation period: the dose differences are typically less than 20% for all sources except ISO where systematically 40-80% of higher doses were observed. Below 200 MeV, a larger discrepancy in dose was found due to the Bragg peak shift caused by different anatomy. The tabulated foetal doses represent the latest and most detailed study to date offering a useful set of data to improve radiation protection dosimetry against external protons.
authors.affiliation: UCSF Comprehensive Cancer Center, University of California, 1600 Divisadero St, Suite H-1031, Box 1708, San Francisco, CA 94115, USA.
authors.forename: Valery
authors.initials: V
authors.lastname: Taranenko
authors.forename: X George
authors.initials: XG
authors.lastname: Xu
mesh_terms: D001822:Body Burden; D003198:Computer Simulation; D004781:Environmental Exposure / Q000032:analysis*; D005260:Female; D006801:Humans; D018811:Maternal Exposure; D008954:Models, Biological; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D011522:Protons; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods* / Q000592:standards
chemical_list: D011522:Protons