# Radiation and Health

> Radiation and health for FMGE Community Medicine: ICRP dose limits, deterministic vs stochastic effects, ALARA, AERB and emergency response.

- Canonical URL: https://prepelephant.com/topics/fmge/community-medicine/radiation-health-fmge
- Exam / course: FMGE · Subject: Community Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Radiation and Health", PrepElephant, https://prepelephant.com/topics/fmge/community-medicine/radiation-health-fmge

## Direct answer

A chest X-ray delivers about 0.02 millisieverts — roughly three days of the natural background radiation every human already absorbs (a global average of 2.4 millisieverts a year, far higher on Kerala's monazite sands) — and that comparison frames radiation protection for exams. The International Commission on Radiological Protection sets occupational limits at 20 millisieverts per year averaged over five years, never exceeding 50 in a single year, with the public limited to 1 millisievert per year; medical exposure of patients sits deliberately outside these limits, governed instead by justification and optimisation. Effects divide into deterministic ones with thresholds (skin erythema, cataract, sterility, acute radiation syndrome) and stochastic ones without thresholds (cancer, heritable effects), and protection rests on ALARA — time, distance and shielding, with the inverse square law doing the arithmetic.

## What you must remember

- **Dose limits (ICRP):** occupational 20 mSv per year averaged over five years (100 mSv in five years), no single year above 50 mSv; public 1 mSv per year; lens of eye occupational limit 20 mSv per year (revised down from 150); declared pregnancy limits fetal dose to 1 mSv thereafter.
- **Units:** absorbed dose in gray (joules per kilogram), equivalent and effective dose in sievert; millisieverts flavour all exam arithmetic.
- **Diagnostic ballpark:** chest X-ray 0.02 mSv, CT chest around 7 mSv — against 2.4 mSv annual natural background.
- **Deterministic effects with thresholds:** temporary sterility about 0.15 Gy, lens opacities around 0.5 Gy, skin erythema about 2 Gy, acute radiation syndrome above about 1 Gy whole body, with LD50/60 near 3-4 Gy untreated.
- **Acute radiation syndrome triad:** prodromal vomiting, latent period, then manifest illness by organ threshold — haematological above 1 Gy, gastrointestinal above about 6-8 Gy, neurovascular above tens of gray.
- **Stochastic effects:** no threshold, probability (not severity) rises with dose; leukaemia latency a few years, solid cancers decades; heritable effects never proven in humans but assumed.
- **ALARA and tools:** minimise time, maximise distance (inverse square law), use lead shielding; TLD badges monitor workers; pregnancy scheduling avoids fetal exposure.
- **Indian and global regulation:** the Atomic Energy Regulatory Board (1983) licenses Indian installations; radon-222 is the second leading cause of lung cancer after smoking; potassium iodide blocks thyroid uptake of radioactive iodine in emergencies (Chernobyl 1986, Fukushima 2011).

## Handling a radiation question the way a radiology resident must

A 26-year-old needs a CT abdomen, and her pregnancy test returns positive. The reasoning is justification versus optimisation: is an ionising study justified at all, can ultrasound or MRI substitute, and if not, can the protocol be dose-reduced? The fetus receives a fraction of the entrance dose and, below 100 mGy, deterministic harm is not expected — the threshold concept doing real clinical work. Now flip to occupational safety: an interventional cardiologist wearing a collar dosimeter and a lead apron works under the fluoroscope; the apron attenuates the body while the unshielded lens accumulates dose — precisely why the eye lens limit was cut to 20 mSv per year. In a nuclear emergency the logic is shelter, evacuation and stable iodine before the plume arrives, as the Chernobyl thyroid-cancer toll among those iodine-unprotected demonstrated.

## Where marks vanish

Students quote 50 mSv as the annual occupational limit forgetting it is the single-year ceiling within the 20-per-year five-year average — the examiner quotes both and asks which applies. The second trap is applying dose limits to patients: no limit applies to justified medical exposure, a conceptual one-liner repeatedly tested. Third, deterministic versus stochastic must be crisp: severity versus probability — deterministic severity rises with dose above a threshold; stochastic probability rises with dose and severity does not. Fourth, remember that sievert already folds in the radiation weighting factor — quoting grays for a neutron question is the planted error. Finally, potassium iodide prophylaxis protects only the thyroid and only from radioactive iodine; it is not a general antidote.

## Frequently asked questions

### What are the ICRP occupational dose limits?
An effective dose of 20 millisieverts per year averaged over five years, with no single year exceeding 50 millisieverts; the public limit is 1 millisievert per year.

### What distinguishes deterministic from stochastic radiation effects?
Deterministic effects have thresholds and their severity rises with dose; stochastic effects have no threshold and their probability rises with dose.

### What does ALARA stand for and what are its practical tools?
As Low As Reasonably Achievable — implemented through minimising time, maximising distance (inverse square law) and using shielding and dose monitoring.

### Which body regulates radiation facilities in India?
The Atomic Energy Regulatory Board, established 1983, which licenses and inspects medical, industrial and research installations.

### Why is potassium iodide given in a nuclear emergency?
Stable iodine saturates the thyroid so radioactive iodine cannot be absorbed, preventing thyroid cancer — as its absence proved after Chernobyl.