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Objective:
In cases where pregnancy is discovered during or after a diagnostic examination, the physician or the patient may request an estimate of the radiation dose received by the fetus as per guidelines and standard operating procedures (SOPs). This study provides the imaging community with dose estimates to the fetus in PET/CT with protocols that are adapted to low dose protocols for patients known to be pregnant from the University of Michigan.

Materials and Methods:
There were nine patients analyzed with data for the first, second and third trimester, the availability of which is quite rare. These images were used to calculate the size-specific dose estimate (SSDE) from the CT scan portion, and the standard uptake value (SUV) and 18F-FDG uptake dose from the PET scan portion using the Medical Internal Radiation Dose (MIRD) formulation. The fetal dose estimates were tested for correlation with each of the following independent measures: gestational age, fetal volume, average water-equivalent diameter of the patient along the length of the fetus, size-specific dose estimate (SSDE), SUV, percentage of dose from FDG . Stepwise multiple linear regression analysis was performed to assess the partial correlation of each variable.

Results:
Fetal self-doses from 18F for the 1st, 2nd and 3rd trimester range from 2.18 mGy (single data point), 0.74-1.82 mGy and 0.017-0.0017 mGy. The combined SSDE and fetal self dose ranges from 1.2-8.2 mGy. These types of images from pregnant patients are rare.

Conclusion:
Our data indicate that the fetal radiation exposure from 18F-FDG PET and CT performed, when medically necessary, in pregnant women with cancer is low. All efforts should be made to minimize the fetal radiation exposure by modifying the protocol appropriately. This is the first study where fetal doses have been determined from CT and PET images.