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After radioactive iodine your body gives off radiation for some days, and some leaves in urine, saliva and sweat. For a while you keep your distance from others, especially babies, young children and anyone pregnant, sleep apart, take care in the toilet and with cups and towels, and stop breastfeeding completely. Your team works out how many days apply to you and writes them down.
Before treatment the patient is told how to protect others and how long it will last, so they can plan (IAEA SRS-63; ICRP 94). Pregnancy is excluded and breastfeeding is stopped completely; ICRP says mothers must cease breastfeeding immediately, and some physicians ask for it to stop two to three weeks before treatment so the breast takes up less iodine (SRS-63). Release is an individual decision: the IAEA and ICRP base it on the dose others could receive rather than on a fixed amount left in the body; the US allows release where no one else is likely to receive more than 5 mSv, with written instructions where anyone could receive more than 1 mSv (10 CFR 35.75); in the UK the patient must have written instructions on restricting others' dose before leaving (IR(ME)R 2017 reg 12(6) and (7)). Many European countries also set a maximum retained activity, mostly 400 to 600 MBq (SRS-63), and thyroid cancer treatment is usually given with a hospital stay there; in the US most patients are now treated as outpatients (87% of survey respondents treated after 2011, Wu 2020).
At home the effort goes on pregnant women, infants and children, because measured doses to adults who follow the advice rarely approach a few millisieverts (SRS-63). The example IAEA leaflet asks for a distance of at least one metre, two metres for longer than an hour, a separate bed two metres apart, close contact limited to half an hour a day, under-twos cared for by someone else, seated urination with flushing and hand washing, a daily shower especially on the first two days, and no sharing of cutlery, crockery, towels or laundry. Durations depend on the activity and on whether the treatment is a first ablation or a later follow-up treatment; the ICRP 94 table reproduced by SRS-63 gives, for 3,700 MBq, 4 days of sleeping apart after a follow-up treatment and 20 days after ablation. Patients carry a card for unplanned admissions and for radiation detectors at airports and borders, which can pick up radioiodine for weeks. ICRP advises women to avoid pregnancy for 4 months after iodine-131 for thyroid cancer; ARSAC in the UK says 6 months; men are commonly advised to avoid fathering a child for some months, on prudence rather than evidence (SRS-63). UK guidance from 2023 found wide variation and some unnecessarily burdensome restrictions, and recommends personalising them.
Why: Knowing in advance how many days of precautions apply makes them easier to follow and less frightening.
“Patients should be given information about their own safety and that of others before their treatment is started.”
Why: Radioactive iodine crosses the placenta and can damage the baby's thyroid; thyroid cancer treatment can usually wait until after pregnancy.
“Pregnancy is a strong contraindication to unsealed radionuclide therapy, unless the therapy is life saving.”
Why: Radioactive iodine passes into breast milk and could destroy the baby's thyroid.
“Thus, therapeutic radiopharmaceuticals, regardless of the route of administration, are potentially hazardous, and therefore breast-feeding must be discontinued indefinitely”
Why: A fixed rule can keep people in hospital who could safely go home, or send home someone who lives with a baby.
“The decision to hospitalize or release a patient should be determined on an individual basis.”
Why: Instructions on paper are there when questions come up at home.
“be provided to the patient or other person specified in paragraph (6) as appropriate prior to the patient leaving the radiological installation where the exposure was carried out.”
Why: Adults at home who follow the advice receive very small doses; the young and the unborn are most sensitive.
“Restrictions, once families and carers have been well instructed, should thus focus on the special consideration groups (i.e. pregnant women, infants and children).”
Why: Radiation falls off quickly with distance, so a little space cuts the dose a lot.
“Do not sit or stay close to any person either at home or at work. Try to maintain a distance of at least one metre. For long periods (more than one hour), stay two metres away.”
Why: A night beside someone is the longest close contact of the day; house walls do not block this radiation well.
“Close contact such as hugging or sex should be limited to half an hour a day. You should sleep in a separate bed. Beds should be two metres apart, even if there is a wall separating them.”
Why: Babies are the most sensitive to radiation and need the longest, closest contact.
“Children under two years old should be looked after by someone else.”
Why: Most of the iodine not taken up by the thyroid leaves in urine; careful toilet habits keep it off surfaces others touch.
“Therefore, pass urine while seated (including men). Always dry your genitals with toilet paper and flush the toilet.”
Why: Some iodine leaves in saliva and sweat; washing removes it.
“Therefore, cutlery, crockery, towels, bed linen, etc., should not be shared with others.”
Why: Emptying the bladder often moves the iodine out of the body sooner and lowers the dose to nearby organs.
“The dose can be reduced by orally hydrating the patient and by encouraging frequent voiding. This is a common recommendation for all patients whether pregnant or not.”
Why: Staff need to know about the radioactivity, and airport and border detectors can pick it up for weeks.
“Environmental or other radiation detection devices are sensitive enough that they will usually detect patients who have received radioiodine treatment for weeks after administration.”
Why: The wait protects a future baby from radiation and lets the team confirm the cancer is controlled before a pregnancy.
“the ICRP recommends that female patients be advised to avoid pregnancy for the time periods indicated in Table 13.”
How care is usually carried out, read from the guidelines and standards cited. Your own team's protocol and their judgement come first; this page is for understanding it, not for doing it yourself.
An individual release decision based on the dose others could receive, with written instructions before leaving (IAEA SRS-63 and SSG-46; ICRP 94; 10 CFR 35.75; IR(ME)R 2017 reg 12), and restrictions focused on pregnant women, infants and children, whose length is set for the person from the activity given and their household rather than taken from a single table. None of these sources grades its advice: the IAEA and ICRP documents are consensus built on measured and modelled doses, and the US and UK texts are law. They differ on two points shown below: how release is decided (dose to others in the US and in IAEA and ICRP advice, a retained-activity limit in many European countries) and how long to avoid pregnancy (4 months ICRP, 6 months ARSAC, 6 to 12 months in some practice). The 2023 UK multidisciplinary guidance adds the case against over-restriction, which its authors found widespread.
International Atomic Energy Agency 2009 · International Atomic Energy Agency, jointly sponsored by PAHO and WHO 2018 · International Commission on Radiological Protection (Annals of the ICRP 34(2)) 2004 · US Nuclear Regulatory Commission (Code of Federal Regulations, via eCFR) 2007 · UK legislation (legislation.gov.uk) 2017 · Wadsley et al. with the British Thyroid Association, British Thyroid Foundation, BNMS, IPEM, BIR, RCR and patient groups (Clinical Oncology) 2023
Where it differs: A patient is kept in hospital until the iodine left in the body falls below a set amount: the old IAEA Basic Safety Standards guidance level was 1,100 MBq; most EU member states use 400 to 600 MBq (range about 95 to 800); Germany 250 MBq, based on 3.5 microsieverts an hour at one metre; the European Thyroid Association favours outpatient treatment up to 800 MBq (SRS-63 tables 9 and 10). Thyroid cancer treatment is usually given with a hospital stay in the EU.
Evidence: SRS-63 says some retained-activity models are unduly conservative and may cause unnecessary hospital stays, and that where the two approaches conflict the ICRP regards the dose-based one as more fundamental.
Where it differs: Release is allowed when no other person is likely to receive more than 5 mSv; written instructions are required when anyone could receive more than 1 mSv, with breastfeeding guidance where a nursing infant could. In practice most US patients with thyroid cancer are treated as outpatients.
Evidence: In a 2018 survey of 1,111 US patients treated between 2011 and 2018, 87% were treated as outpatients (66% before 2009), 67% were able to discuss and individualise their instructions, and 2% did not recall receiving any.
US Nuclear Regulatory Commission (Code of Federal Regulations, via eCFR) 2007 · Wu et al., Journal of Nuclear Medicine 2020
Where it differs: A UK multidisciplinary group convened at the instigation of patient support groups, with the British Thyroid Association, British Nuclear Medicine Society, IPEM, BIR and RCR among the authors, wrote guidance and a patient leaflet focused on personalising the advice, including for patients on haemodialysis.
Evidence: Its abstract reports significant variation across the UK and that some patients are asked to observe unnecessarily burdensome restrictions. Only the abstract was read; its specific day counts are not reproduced here.
Where it differs: Some physicians ask women to stop breastfeeding two to three weeks before radioiodine, so that the breast takes up less iodine and there is no risk of restarting; the general rule is only that breastfeeding stops and does not resume.
Evidence: SRS-63 describes it as a practice some find helpful, without a grade or data.
Where it differs: Gives example tables for working out the number of days of precautions for an individual patient, built on US NRC rules and NCRP Report 155, with a checklist for the patient's circumstances.
Evidence: Its authors state there are insufficient data on long-term outcomes for evidence-based guidelines. Only the abstract was read.
American Thyroid Association Taskforce on Radioiodine Safety (Sisson et al., Thyroid) 2011
| Recommendation | Grade, as printed | Source |
|---|---|---|
| Decide hospital stay or release individually “The decision to hospitalise or release a patient should be determined on an individual basis.” | Consensus (ungraded) | International Commission on Radiological Protection (Annals of the ICRP 34(2)) 2004 |
| Stop breastfeeding immediately after radioiodine “After radioiodine therapy, mothers must cease breastfeeding immediately.” | Consensus (ungraded) | International Commission on Radiological Protection (Annals of the ICRP 34(2)) 2004 |
| Release allowed if no other person is likely to receive more than 5 mSv; written instructions if anyone could receive more than 1 mSv “A licensee may authorize the release from its control of any individual who has been administered unsealed byproduct material or implants containing byproduct material if the total effective dose equivalent to any other individual from exposure to the released individual is not likely to exceed 5 mSv (0.5 rem).” | Regulatory requirement (ungraded) | US Nuclear Regulatory Commission (Code of Federal Regulations, via eCFR) 2007 |
| Written instructions to the patient on restricting others' doses “specify how doses resulting from the patient’s exposure can be restricted as far as reasonably possible so as to protect persons in contact with the patient;” | Regulatory requirement (ungraded) | UK legislation (legislation.gov.uk) 2017 |
| Written instructions to carers after radioiodine, including time and proximity, physical contact and not sharing food or drinks “carer or comforter of the patient (including for example, instructions on time spent with the patient and proximity to the patient, minimizing of physical contact and not sharing food or drinks).” | Safety Guide recommendation (ungraded) | International Atomic Energy Agency, jointly sponsored by PAHO and WHO 2018 |
| Dose constraint of 5 mSv per episode for an adult carer, 1 mSv for children and for the embryo or fetus of a pregnant carer “For an adult carer or comforter, a value of dose constraint commonly used is 5 mSv effective dose per episode.” | Safety Guide recommendation (ungraded) | International Atomic Energy Agency, jointly sponsored by PAHO and WHO 2018 |
Shares Radioactive iodine (I-131), Follicular thyroid cancer, Radioiodine therapy and whole-body iodine scanning, Papillary thyroid cancer.
Shares Radioactive iodine (I-131), Radioiodine therapy and whole-body iodine scanning, Thyroid cancer.
Shares Radioactive iodine (I-131), Radioiodine therapy and whole-body iodine scanning, Thyroid cancer.
Shares Radioiodine therapy (I-131), Radioiodine therapy and whole-body iodine scanning, Thyroid cancer.
Shares Follicular thyroid cancer, Papillary thyroid cancer, Thyroid cancer.
Shares Follicular thyroid cancer, Papillary thyroid cancer, Thyroid cancer.
Shares Radioactive iodine (I-131), Radioiodine therapy and whole-body iodine scanning, Thyroid cancer.