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Radiation protection in nuclear medicine
In nuclear medicine the patient is the radiation source, so protecting staff, family and the public rests on short time, long distance, suitable shielding and contamination control — and distance is the strongest tool, because dose falls with the square of distance.
Why it matters in the exam
The exam includes distance calculations: under the inverse square law, if the dose rate at 2 metres is 6 µSv/h, at one metre it is 24 µSv/h, and at 4 metres it is 1.5 µSv/h. Shielding: for gamma — lead or tungsten (syringe shield and vial shield); for beta — a light material (plastic or acrylic) first, to prevent bremsstrahlung, then lead outside if needed. An ordinary lead apron is almost useless against 511 keV photons in PET, so there the emphasis is time and distance. Average natural background is about 2–3 mSv per year.
Dose limits (ICRP): radiation worker — 20 mSv per year averaged over 5 years, and no more than 50 mSv in any single year; lens of the eye — 20 mSv per year; hands and skin — 500 mSv per year; a pregnant worker — no more than 1 mSv to the fetus from declaration; public — 1 mSv per year. Workers wear a body dosimeter and a finger ring. A patient who received external radiotherapy is not radioactive and does not endanger others — unlike a patient who received I-131 or radioactive seeds.
Patient release after I-131: the decision rests on the expected dose to others — under ICRP 94 up to 5 mSv for a close carer per treatment episode and up to 1 mSv for children and the public — and in practice the dose rate at 1 metre is measured. Home advice: sleeping apart, distance from children and pregnant women for several days, a separate toilet, double flushing, separate utensils and towels. Contamination: gloves, absorbent paper, marking the area, and washing skin with lukewarm water and mild soap without hard scrubbing. Before every study pregnancy and breastfeeding are checked and patient identity and dose are verified.
Key points
- Time, distance, shielding and contamination control.
- Inverse square law: half the distance — 4 times the dose.
- Worker — 20 mSv per year averaged; public — 1 mSv.
- Beta — plastic, then lead.
- Release after I-131 by the expected dose to others.
Summary table
| Topic | Rule | Key number |
|---|---|---|
| Distance | Inverse square law | Half the distance — 4 times the dose |
| Gamma shielding | Lead or tungsten | An apron is ineffective at 511 keV |
| Beta shielding | Light material then lead | Prevents bremsstrahlung |
| Radiation worker | Annual limit | 20 mSv averaged, up to 50 mSv in a year |
| Public | Annual limit | 1 mSv |
| Release after I-131 | Expected dose to others | 5 mSv for a carer, 1 mSv for the public |
A free exam question
מהי מנת הקרינה האפקטיבית המקסימלית )"חסם עליון"( בשנה שאליה מותר למטפלים ולמלווים של נבדק להיחשף? (the question as examined, in Hebrew)
- א. תמונה א
- ב. תמונה ב
- ג. תמונה ג
- ד. תמונה ד
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Sources
- ICRP Publication 103: The 2007 Recommendations of the International Commission on Radiological Protection, 2007 — Dose limits for occupational and public exposure
- ICRP Publication 94: Release of Patients after Therapy with Unsealed Radionuclides, 2004 — Dose constraints for carers and the public
- IAEA Safety Reports Series No. 63: Release of Patients after Radionuclide Therapy, 2009 — Practical guidance
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.
See also: Radiation dose units and ALARA