Radiation dose to the conceptus from multidetector CT during early gestation: a method that allows for variations in maternal body size and conceptus position.

PURPOSE: To develop a method for estimating the radiation dose to the conceptus from multidetector computed tomography (CT) of the abdomen and pelvis in pregnant patients during the first 7 weeks of gestation.
MATERIALS AND METHODS: This study was approved by the institutional review board and informed consent was obtained. A CT simulation software package was used to (a) develop voxelized models on the basis of image data from 117 nonpregnant patients who underwent abdominal and pelvic multidetector CT and (b) calculate dose at a position of the uterus assumed to be the position of the conceptus in case of pregnancy during the first 7 weeks of gestation. Regression analysis was carried out to establish the relationship among conceptus dose, patient body size, and distance from the conceptus to the anterior skin surface.
RESULTS: Normalized conceptus doses calculated by using the software package ranged from 0.335 to 0.785 mGy per absorbed dose to air. Conceptus dose showed a significant correlation with maternal body size and conceptus depth (R² = 0.793, P < .001). A multivariable correlation of conceptus dose normalized to the free-in-air CT dose index (CTDI(F)) with conceptus depth and patient perimeter was produced for estimating conceptus dose from abdominal and pelvic multidetector CT. Conceptus dose data provided for a specific scanner can be applied to other scanners by using correction factors based on ratios between the weighted CT dose index and CTDI(F), resulting in inaccuracies in the estimation of conceptus dose of less than 12%.
CONCLUSION: The radiation dose to the conceptus from abdominal and pelvic multidetector CT can be estimated with a method that allows for variations in maternal body size and conceptus position. © RSNA, 2010.