Pregnant Female Anthropomorphic Dosimetry In Computed Tomography

Date(s) - 04/01/2014
3:00 pm

Matthew Hoerner, PhD Candidate

Over the last twenty five years, medical imaging utilizing ionizing radiation has significantly increased and as a result an individual is more susceptible to receive a higher exposure over the course of his or her lifetime.  Pregnant female diagnostic studies have followed this trend as there has been a 25% increase in Computed Tomography (CT) imaging studies from 1997 to 2006.   An increase in the number studies coupled with newer scanner technology, which has shown to maintain if not raise radiation exposure for a single exam, have resulted in significant increase in individual and collective effective dose.   Most pregnant women that undergo CT exams will receive less than 50 mGy over the course of their pregnancy.  This level of absorbed dose is the established threshold for concern, as it is less than what is needed to induce abnormalities such as growth and mental retardation, which are common effects documented in the epidemiological studies of the Japanese bomb survivors.  However, this level of exposure is comparable to radiation workers who by law require individual monitoring.  The regulation limit set by the Nuclear Regulatory Commission (NRC) is established that no person shall receive more than 50 mSv of radiation dose in a given year.  For an occupational worker who is declared pregnant, the limit is 5mSv per pregnancy cycle or 0.5mSv in one any month.  Given the sensitivity of young children to radiation compared to adults, this discrepancy in monitoring needs to be addressed in some form.

Using anatomically accurate reference physical models and recently developed advanced dosimetry techniques, the absorbed dose to the fetus and embryo will be evaluated at multiple gestation stages from clinical CT studies performed at the conventional imaging protocols using a modern scanner.  The results of these studies are compared to both current biological data to validate or disprove claims about radiation safety in diagnostic radiology, and current clinical fetal/embryonic dosimetry methods.  Most of these resolved uncertainties stem from the effectiveness of tube current modulation imaging and the accuracy of dose calculations using scanner reported DLP values. The manuscript is also intended to advocate any additional imaging precautions, or necessitate new and advanced techniques of monitoring conceptus doses from clinical CT studies.