| dc.description.abstract | Purpose: The purpose of this is study was to compare different methods for estimating the fetal
dose, how much the different methods differ from each other and on which dose
levels the fetal doses are estimated to.
Theory: A radiological procedure should always be justified and in the case of a pregnant
patient the justification should include both the mother and the fetus. The absorbed
dose to the fetus should be considered in the planning procedure, which means that
you need to be aware of the potential fetal dose in advance. There are some risks
associated with ionizing radiation for the fetus during pregnancy. These risks can be
related to which stage of the pregnancy the woman is in and to the absorbed dose of
the fetus. The associated risks are the deterministic effects which have a 100-200
mGy threshold and increase with the dose, these effects include abnormalities and
mental impairments, and the stochastic effects which is the increased risk of inducing
cancer. The doses in radiology are under normal circumstances low, but during CT
examinations there is a risk that the fetal dose increases either in a single examination
or repeated examinations, and for those cases a more accurate fetal dose estimation is
necessary. If the dose is high and there is a high uncertainty in the dose calculations,
there is a risk that the dose might come near or exceed the threshold value. In those
cases, it is important to know which dose estimation method to use.
Method: To estimate the fetal dose, data from female pregnant patients CT examinations and
phantom measurements were retrospectively used to estimate the fetal dose using
different methods and programs. The patients were categorized into groups depending
on the scan protocol and trimester, because the scan range and parameters are similar
for each protocol. The different estimation methods and quantities that were used was
CTDIvol, SSDE, CT-Expo, CODE and VirtualDoseCT. The methods differ in their
calculations, some of them take consideration to the patient’s size and some of them
the trimester or pregnancy week. The results from these methods and quantities were
approximated to the fetal absorbed dose for comparison. The phantom measurement
was made to compare the different dose estimation methods on the same “patient”
during the same circumstances and to compare the results of fetal dose estimations
from the patient measurements with a reference. | sv |
