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Foetal dose estimation

Introduction

Every clinical diagnostic medical physicist will be called upon to estimate the radiation dose to the foetus either prospectively or retrospectively so the radiologist and referring physician can determine the appropriate action relative to x-ray examinations.  However, the medical physicist must also provide guidance regarding the risk to the fetus.  Consequently, the medical physicist must understand the issues of radiosensitivity relative to gestational age and the normal risks during pregnancy. 

Important Principles

The first issue in estimating foetal dose is determination of the number of x-ray examinations and projections, and the location of the foetus relative to the x-ray beam.  This can be accomplished by reviewing the films or digital images.  Next, one must estimate the entrance dose to the patient based on information for digital images or records which may be available with technique factors for this patient.  This information is then used to estimate the foetal dose using software or tables available in the literature.

The medical physicist must provide estimates of the risk of the radiation dose to the foetus.  This is relatively complicated since it is based on foetal age.  Other considerations include the risk of naturally occurring birth complications and defects, as well as other factors such as alcohol and caffeine consumption, and the use of recreational (illicit)  or legal drugs (including contrast media).  These all impact the risk of a foetal abnormality or miscarriage.

If the request for foetal dosimetry is prospective, the medical physicist must provide recommendations on methods for the minimization of the dose to the foetus.  What can be done to reduce the radiation dose such limit the number of images, use higher speed image receptors, or, perhaps, consider the use of non-ionizing radiation examinations such as ultrasound or magnetic resonance imaging?

It is uncommon that the x-ray examination should be delayed due to pregnancy assuming the information is medically indicated and necessary at the time for diagnosis or treatment of the patient.  Consequently, the expertise of the medical physicist is very important to the radiologist and referring physician.

Introduction to References

The attached references provide a brief overview of foetal radiation dose estimation and risk.  

Software is available for specific organ dose calculation from STUK and ImPact, as well as other sources and is discussed in the paper by Osei.