Background: In recommending the occupational dose limit of ionizing radiation for pregnant women, the International Commission on Radiological Protection apparently assumes that the dose to the conceptus from ionizing radiation exposure is about half the dose at the surface of the mother's abdomen.
Methods: To test this assumption with respect to galactic cosmic radiation, calculations were made using FAA computer program CARI-LF2, which calculates equivalent doses from galactic cosmic rays at selected depths in soft tissue at any specified location in the atmosphere or on user-entered flight profiles.
Results: The calculations showed that the equivalent dose of galactic radiation was almost the same at all depths.
Conclusions: Thus the assumption of considerable shielding of the conceptus being provided by the woman's body is not correct with respect to galactic cosmic radiation, the principal type of radiation to which aircrews are exposed. The effective dose as calculated with FAA computer program CARI-5E, which calculates effective dose in an anthropomorphic phantom at any specified location in the atmosphere or on user-entered flight profiles, was found to be a good estimate of the equivalent dose at the depth of the conceptus.