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Nuclear Medicine

Health consumers information

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 mSva.

 Test Radiopharmaceutical  Advice to patient concerning the need to restrict close contact with a childb Advice to patient concerning the need to interrupt breastfeedingc
PET 18F-FDG Not required 1 hr interruption
Gallium 67Ga-citrate Restrict contact for 3 days Cessation1
Lung perfusion 99mTc-MAA Not required 13 hr interruption
Bone 99mTc-MDP or HDP Restrict contact for 1 hr 1 hr interruption
Heart , tumour or parathyroid 99mTc-MIBI Restrict contact for 4 hr 4 hr interruption
Thyroid 99mTc-pertechnetate Not required 26 hr interruption
Meckel’s diverticulum 99mTc-pertechnetate Not required 34 hr interruption
Red blood cell label 99mTc-PYP Not required 2 hr interruption
In vitro in vivo labelled 99mTc-red cells Restrict contact for 2 hr 12 hr interruption
Heart 99mTc-tetrofosmind Restrict contact for 4 hr 4 hr interruption
Infection/inflammation 99mTc-white cellse Not required 24 hr interruption
Tumour 111In-octreotide Restrict contact for 42 hr 45 hr interruption
Tumour 123I-MIBGf Not required 22 hr interruption
Thyroid 123I-sodium iodide Not required 6 hr interruption
Perfusion imaging 125I-HSA Not required 6 day interruption
Thyroid –
post-ablation		 131I-sodium iodide Restrict contact for 6 hr Cessation
Heart or tumour 201Tl-chloride Not required 15 hr interruption

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.

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