Case of radioactive iodine exposure during pregnancy

Radiation Safety and Accidental Radiation Exposures in Nuclear Medicine

Medical radiation accidents and unintended events may lead to accidental or unintended medical exposure of patients and exposure of staff or the public. Most unintended exposures in nuclear medicine will lead to a small increase in risk; nevertheless, these require investigation and a clinical and dosimetric assessment. Nuclear medicine staff are exposed to radiation emitted directly by radiopharmaceuticals and by patients after administration of radiopharmaceuticals. This is particularly relevant in PET, due to the penetrating 511 keV γ-rays. Dose constraints should be set for planning the exposure of individuals. Staff body doses of 1-25 µSv/GBq are reported for PET imaging, the largest component being from the injection. The preparation and administration of radiopharmaceuticals can lead to high doses to the hands, challenging dose limits for radionuclides such as ⁹⁰Y and even ¹⁸F. The risks of contamination can be minimized by basic precautions, such as carrying out manipulations in purpose-built facilities, wearing protective clothing, especially gloves, and removing contaminated gloves or any skin contamination as quickly as possible. Airborne contamination is a potential problem when handling radioisotopes of iodine or administering radioaerosols. Manipulating radiopharmaceuticals in laminar air flow cabinets, and appropriate premises ventilation are necessary to improve safety levels. Ensuring patient safety and minimizing the risk of incidents require efficient overall quality management. Critical aspects include: the booking process, particularly if qualified medical supervision is not present; administration of radiopharmaceuticals to patients, with the risk of misadministration or extravasation; management of patients' data and images by information technology systems, considering the possibility of misalignment between patient personal data and clinical information. Prevention of possible mistakes in patient identification or in the management of patients with similar names requires particular attention. Appropriate management of pregnant or breast-feeding patients is another important aspect of radiation safety. In radiopharmacy activities, strict quality assurance should be implemented at all operational levels, in addition to adherence to national and international regulations and guidelines. This includes not only administrative aspects, like checking the request/prescription, patient's data and the details of the requested procedure, but also quantitative tests according to national/international pharmacopoeias, and measuring the dispensed activity with a calibrated activity meter prior to administration. In therapy with radionuclides, skin tissue reactions can occur following extravasation, which can result in localized doses of tens of Grays. Other relevant incidents include confusion of products for patients administered at the same time or malfunction of administration devices. Furthermore, errors in internal radiation dosimetry calculations for treatment planning may lead to under or over-treatment. According to literature, proper instructions are fundamental to keep effective dose to caregivers and family members after patient discharge below the Dose constraints. The IAEA Basic Safety Standards require measures to minimize the likelihood of any unintended or accidental medical exposures and reporting any radiation incident. The relative complexity of nuclear medicine practice presents many possibilities for errors. It is therefore important that all activities are performed according to well established procedures, and that all actions are supported by regular quality assurance/QC procedures.

Effects of fetal involvement of inadvertent radioactive iodine therapy for the treatment of thyroid diseases during an unsuspected pregnancy

Radioactive iodine (¹³¹I) therapy is absolutely contraindicated in pregnancy, but reports of inadvertent exposure continue to appear in the literature. Radiation-induced effects on the embryo/fetus are highly dependent on the stage of pregnancy, the dose absorbed by the embryo/fetus, and the manifestations of the pathological condition that develops as a result of the irradiation. Prior to implantation, the major concern is death of the embryo when exposed to radiation greater than the 100 mGy threshold. At this very early stage of pregnancy, exposure to ¹³¹I is unlikely to cause major malformations or thyroid dysfunction in surviving embryos. Exposure during organogenesis of the thyroid (from 10 weeks of gestation onward) and that of other organs at radiation thresholds of 100-300 mGy may result in fetal thyroid ablation, malformations, growth restriction, and in later life, mental retardation (MR). In addition, any dose of radiation exposure may increase the risk of cancer many years after the in utero exposure. Fetal and neonatal hypothyroidism due to in utero ¹³¹I exposure may require lifelong thyroxine replacement therapy and result in severe MR if the condition is not recognized immediately. Therefore, thyroid function must be evaluated and replacement therapy should be started without delay even before birth. Physicians treating women of childbearing age with ¹³¹I need to be aware of the risks of in utero ¹³¹I exposure and take all measures to avoid inadvertent exposure during pregnancy. Nevertheless, in case of accidental exposure, the clinician should confirm the gestational age at exposure, evaluate the risks to the fetus by estimating the radiation dose delivered, and discuss the subsequent management plan with the pregnant woman. This review aimed to summarize the current knowledge regarding the risk of harm to the developing fetus after in utero ¹³¹I exposure, especially focusing on the effects on thyroid function. This study also evaluated the most significant new findings regarding the prevention and in utero and peripartum management of fetal exposure to ¹³¹I.