# Radiation safety at home after radioactive iodine (I-131) for thyroid cancer

Source: https://onco.cc/protocols/radioiodine-therapy-home-radiation-safety/  
OnCo record `radioiodine-therapy-home-radiation-safety` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

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.

## Summary

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.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: radioactive iodine precautions; RAI precautions; I-131 home precautions; radioiodine ablation precautions; after radioiodine treatment at home; radioiodine isolation; radioactive iodine and children; radioiodine and pregnancy; radioiodine and breastfeeding

## Connected records

- protocols: [Radiation safety at home after lutetium-177 PSMA or dotatate therapy](https://onco.cc/protocols/lutetium-177-therapy-home-radiation-safety/), [Release of patients after radionuclide therapy or a permanent implant: criteria, instructions and records](https://onco.cc/protocols/radionuclide-therapy-patient-release-criteria/)
- cancers: [Follicular thyroid cancer](https://onco.cc/cancers/follicular-thyroid-cancer/), [Papillary thyroid cancer](https://onco.cc/cancers/papillary-thyroid-cancer/), [Thyroid cancer](https://onco.cc/cancers/thyroid/)
- technologies: [Radioiodine therapy and whole-body iodine scanning](https://onco.cc/technologies/radioiodine-therapy/)
- drugs: [Radioactive iodine (I-131)](https://onco.cc/drugs/radioactive-iodine/)
- institutions: [International Atomic Energy Agency: Rays of Hope](https://onco.cc/institutions/iaea/)
- terms: [Radioiodine therapy (I-131)](https://onco.cc/terms/radioiodine-term/)

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