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Fetal dose in radiotherapy




Introduction

Radiation is a known teratogen, i.e. causes birth defects, and may induce cancer. The effects of radiation on the fetus depend on the dose to the fetus and the stage of development at the time of exposure. Pregnancy is generally not a contraindication to radiation therapy in patients with cancer remote from the pelvis because appropriate shielding can reduce the fetal dose sufficiently.

Important Principles

A crude estimate of the dose to the fetus can be obtained from published data. Because of approximations in these data, discrepancies between calculated estimates and actual measurements may occur. Often a considerable reduction in fetal dose can be obtained by designing a special shield. Shielding material can either be placed on the couch, on a special construction that can be placed over the patient, or positioned on the blocking tray of the linac. It is important to measure in vivo the fetal dose, e.g. at the top of the fundus, the umbilicus, and the symphysis, throughout the expected range of fetal growth. When applying IMRT, an additional step to reduce the fetal dose is to optimize the IMRT treatment plan with as few monitor units as possible.

Introduction to References

The ICRP Report describes the biological effects of radiation on the fetus in detail. The AAPM Report presents data and techniques to estimate the radiation dose the fetus will receive when women are treated with radiotherapy during pregnancy. Designs for simple to more complex types of shielding equipment are also described to reduce the fetal dose with appropriate shielding. The publication of Kry et al. gives practical information complimentary to the AAPM Report, while the paper of Josipović. et al. elucidates the specific problems when applying IMRT treatment techniques.