Nuclear Medicine and the Pregnant Patient Q&A

1. Can a diagnostic nuclear medicine exam be performed on a woman of childbearing age?
2. In what way do nuclear medicine exams differ from x-ray exams for pregnant or potentially pregnant patients?
3. Is a nuclear medicine procedure safe if performed during pregnancy? If so, are there any precautions that could reduce radiation exposure to the unborn child?
4. What are the typical fetal doses from nuclear medicine procedures?
5. Is a therapeutic nuclear medicine procedure safe if performed during pregnancy?
6. What actions should be taken if a patient undergoes radioiodine therapy and is later found to be pregnant?
7. Can a pregnant woman be around a family member who is treated with radioiodine?
8. How long should a woman wait to become pregnant after radionuclide therapy?
9. Can a nuclear medicine technologist continue working during pregnancy?
10. Can the patient or nuclear medicine technologist who is breast-feeding continue to work?
11. What do I tell a patient who is planning to become pregnant soon after the nuclear medicine exam?

Q

Can a diagnostic nuclear medicine exam be performed on a woman of childbearing age?

A

Yes. The possibility of pregnancy should be assessed and, if pregnancy is likely, justification for the exam should be reevaluated to determine whether another, nonradiation test could be used and how necessary the results are to the health of the patient.

If there is any question regarding pregnancy status and the exam must be performed, a pregnancy test is recommended so that the patient can be adequately informed of the possible risks to the unborn child prior to the exam.

Q

In what way do nuclear medicine exams differ from x-ray exams for pregnant or potentially pregnant patients?

A

The 10-day rule was established by the International Commission on Radiological Protection to minimize the potential for performing x-ray exams on pregnant women. The basis of the rule was to do abdominal and pelvic x-ray exams only during the 10 days following the onset of menstruation. We know much more today about radiation and pregnancy, and we know that substantial doses (~10 rem; more than is received from routine diagnostic medical x-ray exams) are necessary to cause birth defects or malformations. Since organogenesis starts 3 to 5 weeks postconception, it was felt that radiation exposure in early pregnancy couldn't result in malformation. Now the focus is shifted to a missed period and the possibility of pregnancy. If there is a missed period, a female should be considered pregnant unless proved otherwise. In such a situation, every care should be taken to explore other methods of getting the clinical information by performing exams that do not use ionizing radiation.

Q

Is a nuclear medicine procedure safe if performed during pregnancy? If so, are there any precautions that could reduce radiation exposure to the unborn child?

A

Yes, nuclear medicine procedures performed during pregnancy can be safe, particularly those that are diagnostic in nature. Obviously, there must be strong justification for the procedure and the risks and benefits must be explained to the patient. If another procedure, one not involving radiation, could be performed and provide the same clinical information, that would be recommended.

The primary method to reduce radiation exposure to the unborn child is to strongly recommend to the mother that she drink a lot of fluid (water preferably). Increased hydration and frequent urination can reduce the radiation dose substantially.

Sometimes, if it is not uncomfortable for the mother to lie on the scan table for a longer imaging time, smaller amounts of radioactive material can be administered. If a smaller activity is administered, it is important that the imaging time is lengthened to assure the same diagnostic quality of the images.

Q

What are the typical fetal doses from nuclear medicine procedures?

A

The table below gives ranges of fetal dose based on the administered activity to the mother. Most diagnostic nuclear medicine procedures give a small radiation dose (a few mGy), although the ⁶⁷Ga used to look for abscesses or tumors can give a higher dose (tens of mGy).

Fetal Whole-Body Dose from Common Nuclear Medicine Examinations in Pregnancy¹

¹Adapted from Russell, Stabin, Sparks et al., 1997; Wagner, Lester, Saldana et al., 1997; ICRP 53; and ICRP 80
²Fetal thyroid doses are much higher than fetal whole-body dose, e.g., 5-15 mGy/MBq for ¹²³I and 0.5-1.1 Gy/MBq for ¹³¹I if the thyroid is present (roughly after week 8-10 of gestation).

Q

Is a therapeutic nuclear medicine procedure safe if performed during pregnancy?

A

It is preferable that a woman who is pregnant not undergo therapeutic nuclear medicine procedures unless there are implications for her safety (i.e., to save her life). If the procedure must be performed, the possible fetal radiation dose should be calculated and, from that dose, the risk of malformations and childhood cancer should be estimated. This information should be shared with the patient.

If the procedure can be delayed until after delivery, the patient's physician needs to know that many radioactive materials (including the often-used radioiodine for thyroid carcinoma) can be excreted in breast milk. The physician should recommend cessation of breast-feeding in these cases.

Q

What actions should be taken if a patient undergoes radioiodine therapy and is later found to be pregnant?

A

The answer depends on the age of the fetus and the calculated radiation dose to the fetus and the fetal thyroid. If the fetus is less than eight weeks, it is unlikely that the thyroid has formed so the whole-body fetal radiation dose will be of interest. The whole-body fetal doses from a 3,700 GBq (about 100,000 mCi) administered radioiodine dose to the mother will be in the range to cause a spontaneous abortion (usually referenced as 100 mGy or more). Up to six weeks, the whole-body dose (from 3,700 GBq) is 100–150 mGy and for weeks 7–9 the whole body dose is 850-900 mGy. If the fetus remains viable after this time, then there are no further expected harmful effects (this is a time called the "all or none" period, where the radiation either causes a spontaneous abortion if the dose is high enough or the radiation dose will cause no harm at all).

After week eight, the fetal thyroid may be present and will accumulate radioiodine. This leads to a significant radiation dose to the thyroid because there is such a small amount of thyroid tissue present. If it is possible and can be done shortly after the radioiodine administration (within 12 hours or so), stable potassium iodide (KI) could be given to partially block both the maternal and fetal thyroids mitigating the large fetal thyroid dose. Note that administering KI will reduce the radiation dose to the mother's thyroid, possibly negating the desired therapeutic effect.

The estimated whole-body doses post-eight weeks for an administered dose of 3,700 GBq (about 100,000 mCi) are 220 mGy @ 2–4 m; 110 mGy @ 6–9 m. The estimated fetal thyroid tissue doses for an administered dose of 3,700 GBq (about 100,000 mCi) are 760 Gy @ 11 w; 880–2,200 Gy @ 4 – 5 m; 2,000 – 3,200 Gy @ 7 – 9 m. (Take special note that these thyroid dose estimates are all in units of gray, not milligray.)

Q

Can a pregnant woman be around a family member who is treated with radioiodine?

A

Yes, there is no risk from external radiation exposure. Patients treated with radioiodine and released from the hospital must meet certain regulatory restrictions. The total radiation exposure that a family member or caregiver can receive from a patient released from the hospital is 500 mrem (or 5 millisievert). This radiation dose is well below the radiation doses known to cause fetal effects (by at least an order of magnitude).

The guideline to follow when living in the same quarters as a patient who had radioiodine therapy is not to use the same utensils or same toilet, share food, or have skin-to-skin contact with the patient, as the radioiodine will be on the skin and in the saliva of the patient. These restrictions would apply for seven days.

Q

How long should a woman wait to become pregnant after radionuclide therapy?

A

The International Commission on Radiation Protection (ICRP Report 84, Pregnancy and Radiation) suggests not becoming pregnant for about six months after the treatment. The issue is not one of possible genetic effects. The delay is recommended, in part, because of possible additional medical follow-up for the disease being treated. It is best to assure all necessary medical treatments (with radioactive materials) are completed prior to getting pregnant. It is also recommended because, according to ICRP, enough radioiodine would be gone from the mother's body by that time, assuring the fetal dose is very small.

In cases where ³²P, ⁸⁹Sr, or ¹³¹I MiBG (meta iodobenzylguanidine) is used for therapy, ICRP recommends waiting 3, 24, and 3 months, respectively, to assure the fetal dose is very small.

Q

Can a nuclear medicine technologist continue working during pregnancy?

A

Yes. By limiting close patient contact, the radiation doses received by nuclear medicine technologists are low. Considerations should be made for possibly limiting certain types of work or the amount of time spent in particular activities, including the administration of therapeutic radioiodine, daily work in a nuclear pharmacy, and work with PET radiopharmaceuticals. A review of the worker's past dosimetry records will help determine if work must be limited.

Restricting the individual from administrations of therapeutic radioiodine should be considered because, as in the case of a pregnant patient, the fetus could receive a high radiation dose from an accidental uptake by the mother. Limiting the amount of time working in a nuclear pharmacy might be necessary, as these nuclear medicine technologists tend to receive higher radiation doses due to the higher activities handled. A review of the technologist's dosimeter readings should be undertaken to determine whether limitation is necessary.

Q

Can the patient or nuclear medicine technologist who is breast-feeding continue to work?

A

Some recommendations and regulations indicate that, after certain nuclear medicine procedures, patients should be told to stop breast-feeding for some period of time. The table below shows some examples of recommended cessation times.

Adapted from the U.S. Nuclear Regulatory Commission NUREG 1556, Vol. 9, Appendix U, October 2002.

A nuclear medicine technologist who is breast-feeding can continue her nuclear medicine duties and can continue breast-feeding. Uptake of radioactive material by the mother and subsequent excretion into the breast milk is not expected.

Q

What do I tell a patient who is planning to become pregnant soon after the nuclear medicine exam?

A

For diagnostic nuclear medicine exams, becoming pregnant soon after the procedure poses no issues. It is only with the therapeutic agents that planning needs to occur. Recommendations of the ICRP are that women do not become pregnant until the estimated fetal dose falls below 1 mGy (100 mrem). The recommended delay after the therapeutic agents is six months (see the answer to question 8).