Nuclear Medicine

Author: Dr Timothy Cain*

What are the precautions for children and pregnant patients who require a nuclear medicine procedure?

• Nuclear medicine studies are frequently used in children, and the dose of the administered radiopharmaceutical is adjusted to the patient’s weight. As for all imaging studies involving ionising radiation, it is important that careful consideration is given to carrying out an alternate test that does not involve ionising radiation (such as ultrasound or MRI). The radiation dose received from bone scans and renal scans is minimised by encouraging the patient to drink more clear fluid after the test.
• Imaging of pregnant patients with ionising radiation from X-rays, CT scans and nuclear medicine studies is generally avoided if possible. When it is required, it is usually carried out after close discussion with the supervising nuclear medicine specialist. Pregnant patients do sometimes have nuclear medicine studies, but this is usually in the context of possible pulmonary thrombo-embolism (PE). The radiation dose and associated risk to the patient and foetus from a lung scan in this circumstance is small in comparison to the risk of not diagnosing a PE. The dose administered is usually adjusted to minimise the radiation dose further.

What are the precautions for lactating patients and patients looking after small children, who require a Nuclear Medicine procedure?

A child consuming breast milk from a patient who has had a nuclear medicine study might receive an unnecessary radiation dose if there has been insufficient time between the nuclear medicine study and breast-feeding. Similarly, children in close contact with the patient might receive an unnecessary radiation dose.

It is only the radioactivity of the breast milk that is an issue; the other components of the radiopharmaceutical, from diagnostic nuclear medicine studies, are not considered harmful. Once the radioactivity has reduced, the breast milk can be consumed normally by the baby.

In the table below:

• The times vary according to the likelihood that the radiopharmaceutical administered will get into the breast milk, and the energy of the ionizing radiation emitted from the radiopharmaceutical.
• Cessation means stopping breast-feeding completely, as the period of interruption recommended is likely to make continuation of breast-feeding difficult. Please discuss this with the nuclear medicine specialist.
• Interrupting means do not breast-feed until the specified number of hours has elapsed from the time of administration of the radiopharmaceutical. This gives time for the radioactivity of the radiopharmaceutical to reduce to an acceptable level by radioactive decay. Importantly, breast milk expressed during this period of interruption can be stored for use after the recommended time period of interruption has elapsed.
• Additionally, close contact with children should be minimized wherever possible for the recommended period of time. A distance of 2–3 metres should be maintained between the patient who received the radiopharmaceutical and any children.

The following table is a summary of advice regarding the need to restrict close contact with an infant and/or the need to interrupt breast-feeding to ensure that the infant receives a total effective dose (from both external and internal irradiation) of no more than 1 mSv^a.

Modified from:  ARPANSA – Radiation Protection Series No 14.2. Date of publication: 8 August 2008 pgs 31-32.
^aOther agents do not require restriction of contact with small children or interruption of breast-feeding. These include those agents used for white cell scans (^99mTc-colloid), biliary scans (^99mTc-DISIDA or HIDA), renal scans (^99mTc-DMSA or ^99mTc-DTPA or ^99mTc-MAG3), GFR estimation (⁵¹Cr-EDTA), lung (ventilation only) scans (^99mTc-aerosol or Technegas) and ¹¹¹In-white cell scans.

Notes:

a. This table gives estimates of the minimum close contact restriction or interruption period required to limit the dose to less than 1 mSv. Where the restriction or interruption period calculated is very short (e.g. for 18F-FDG), or is indicated as not required, it might be prudent to apply a restriction or interruption period of at least 4 hours for ALARA (as low as reasonably achievable) purposes.
b. Takes into account external exposure from the patient only. The contact restriction times specified are post-administration (i.e. the time lapse from the time the radiopharmaceutical is administered to the patient to the resumption of normal contact). Concentration of radioactivity is measured in kilo Becquerels per millilitre.
c. Takes into account both external exposure from the mother, and internal dose from ingested milk. The interruption periods specified are post-administration.
d. There is a lack of scientific data relating to the uptake and clearance of ^99mTc-tetrofosmin from breast milk. For the purposes of these calculations, it has been assumed that its behaviour in vivo is similar to that of ^99mTc-MIBI.
e. Assumes a labelling efficiency of greater than 75%.
f. Assumes the chemical species appearing in the breast milk is ¹²³I-sodium iodide.

¹Available from ARPANSA web site: www.arpansa.gov.au/publications/codes/rps14_2.cfm

*The author has no conflict of interest with this topic.

Page last modified on 26/7/2017.