Abstract
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. This study provides the imaging community with dose estimates to the fetus in PET/CT based on patient data for 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 perimeter of the pregnant patient along fetal length, fetal depth average water-equivalent diameter of the patient along the length of the fetus, size-specific dose estimate (SSDE) using only known CTDIvol, SUV, percentage of dose from FDG for cases of known CTDIvol. Stepwise multiple linear regression analysis was performed to assess the partial correlation of each variable. This is the first study where fetal doses have been determined from CT and PET images. Fetal self-dose from 18F for the 1st, 2nd and 3rd trimester range from 2.18 mGy, 0.74-1.82 mGy and 0.017-0.0017 mGy. The range of SSDE and fetal self dose ranges from 1.2-3.0 mGy. These types of images from pregnant patients are rare. 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.
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