893
edits
Changes
Jump to navigation
Jump to search
→Pregnant Patients Undergoing Radiation Therapy
[[Radiation therapy]] (whether with external beam, brachytherapy, or nuclear medicine) can involve high radiation doses and may cause harm to the fetus. The risk to the fetus is dependent on the stage of fetal development. Lethal risk occurs in the pre-implantation phase, malformation occurs during major fetal organogenesis 3–7 weeks post implantation, mental retardation occurs at 8–15 weeks post implantation, and future cancer risk follows a stochastic model. Although there is variability in threshold radiation doses, it can be generalised that risks become notable at fetal doses of 100 mGy (10 rad) or above. So, it is essential to ascertain whether a female patient is pregnant prior to [[radiation therapy]]. In pregnant patients, cancers that are remote from the pelvis can usually be treated with radiation therapy. However, this requires careful planning. Cancers in the pelvis cannot be treated adequately during pregnancy without severe or lethal consequences for the embryo/fetus. [[radiation therapy]] in pregnant patients requires pre-therapy fetal dosimetry estimation followed by a comprehensive discussion of the benefits and risks of the procedure, with the patient included as part of the informed consent process.
It should also be noted that <sup>131</sup>I used for diagnostic or therapeutic purposes and <sup>32</sup>P used for therapeutic purposes, should be avoided in pregnant patients because iodine and phosphor can cross the placental barrier readily. The fetal thyroid is sufficiently mature to concentrate iodine at approximately 10 weeks post implantation, and there is a risk of causing fetal hypothyroidism ([[ICRP Publication 84]] Pregnancy and Medical Radiation). <ref name="Pub084"/> As a rule, a pregnant patient should not be treated with a radioactive substance unless the radionuclide therapy is required to save her life: in that extremely rare event, the potential absorbed dose and risk to the fetus should be estimated and conveyed to the patient and the referring Physician. Considerations may include terminating the pregnancy ([[ICRP Publication 84]] Pregnancy and Medical Radiation).<ref name="Pub084"/>
Termination of pregnancy is an individual decision affected by many factors. Absorbed doses below 100 mGy to the developing embryo/fetus should not be considered a reason for terminating a pregnancy. At doses to the embryo/fetus above this level, informed decisions should be made based upon individual circumstances, including the magnitude of the estimated dose to the embryo/fetus, and the consequent risks of harm to the developing embryo/fetus and risks of cancer in later life.
