Radiation dose and protection

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Beginner

X-rays are ionising radiation. At the doses used for plain radiographs the risk to an individual is very small, but it is not zero, and doses add up across a lifetime and across a population. Anyone who requests, performs or interprets X-rays should be able to answer two questions: how big is the dose compared with everyday life? and is this exposure justified? In the UK, the second question is a legal requirement under the Ionising Radiation (Medical Exposure) Regulations 2017, known as IR(ME)R. This page explains typical doses, the principles of protection, pregnancy checks and the change in thinking about lead shielding.

1. Dose basics

The quantity most often quoted for patients is the effective dose, measured in millisieverts (mSv). It estimates the overall stochastic risk of an exposure by weighting the dose to each organ by that organ's sensitivity. It is useful for comparing examinations and for explaining risk, but it is an approximation for a reference person, not a precise measure for an individual.

Radiation can cause two kinds of effect:

• Deterministic (tissue) effects, such as skin injury or cataract, occur only above a threshold dose, and their severity increases with dose. Diagnostic plain films are far below these thresholds; long interventional procedures can approach them.
• Stochastic effects, chiefly cancer induction, have no known safe threshold. The probability, not the severity, is assumed to rise with dose. Radiation protection is built on the cautious assumption that even small doses carry a proportionally small risk.

Children are more sensitive to radiation than adults and have longer to live in which a cancer could develop, so paediatric doses deserve extra care.

2. Typical doses compared

A helpful way to explain dose is to compare it with natural background radiation, which everyone receives from rocks, soil, radon gas, cosmic rays and food. In the UK this averages a few mSv per year. The figures below are approximate typical adult values from UKHSA data; real doses vary with the patient's size, the equipment and the technique.

Examination	Typical effective dose	Roughly equivalent background
Chest X-ray (PA)	About 0.014–0.02 mSv	2–3 days
Abdominal X-ray	About 0.4–0.7 mSv	2–3 months
Lumbar spine X-ray	About 0.7 mSv	About 3–4 months
CT chest	About 6–7 mSv	About 3 years
CT abdomen and pelvis	About 10 mSv	About 3–4 years

Figures vary between sources and with technique [VARIES]. The important message is the scale: a chest X-ray is a very low-dose test, an abdominal film is many times higher, and CT is higher again, by one to two orders of magnitude compared with a chest film. Extremity films (hands, feet) have very low effective doses because little radiosensitive tissue is exposed.

3. Justification and optimisation (ALARP)

Medical radiation protection rests on two principles:

• Justification. The expected benefit of the exposure to the patient must outweigh the risk. Would the result change management? Has the question already been answered by a recent film? Would ultrasound or MRI, which use no ionising radiation, answer it as well? The RCR's iRefer guidance helps referrers choose the right test.
• Optimisation. Once justified, the dose must be kept as low as reasonably practicable (ALARP), the UK term, while still producing an image that answers the question. In the US the equivalent phrase is ALARA ("achievable"). Optimisation includes correct exposure factors, tight collimation, good positioning to avoid repeats, and appropriate equipment settings.

Unlike occupational exposure, there is no dose limit for patients. A limit would make no sense: a patient with major trauma may need several CT scans. The protection comes from justifying each exposure and optimising it.

4. IR(ME)R: who does what

IR(ME)R 2017 sets out duty holders, each with specific legal responsibilities:

Duty holder	Responsibility
Employer	Provides the framework: written procedures, protocols, training records, and entitlement of staff to act in each role.
Referrer	A registered healthcare professional entitled to request the exposure. Must supply enough clinical information for it to be justified.
Practitioner	Takes responsibility for justifying the individual exposure (often a radiologist or radiographer, sometimes under written guidelines).
Operator	Carries out practical aspects of the exposure, such as positioning, setting factors and checking identity. Radiographers are the usual operators; others may be entitled for specific tasks.

For referrers, the practical point is that a request with no meaningful clinical question ("?pathology", "routine") may be rejected because it cannot be justified. Write the question you want answered.

Before any exposure, the operator confirms the patient's identity and checks that the examination matches the request. Exposures given to the wrong patient, the wrong body part or much more than intended may need to be reported under IR(ME)R as significant accidental or unintended exposures.

5. Pregnancy checks

The developing fetus is particularly sensitive to radiation. UK practice is to ask individuals of childbearing potential, typically aged about 12–55, whether they are or might be pregnant before an exposure in which the primary beam irradiates the abdomen or pelvis, or which may otherwise give a significant fetal dose. The Society of Radiographers and RCR promote the "Pause and Check" approach to these and other pre-exposure checks.

• Some departments apply the 28-day rule for low-dose examinations (proceed if the patient is not known to be pregnant, unless a period is overdue) and the 10-day rule for higher-dose examinations of the abdomen and pelvis (schedule within 10 days of the start of the last period). Policies differ [LOCAL]; follow your department's protocol.
• Examinations of the chest, limbs and head deliver a very small fetal dose and are usually acceptable during pregnancy when clinically needed. Do not withhold a clinically justified chest X-ray from a pregnant patient with suspected pneumonia or pneumothorax.
• If pregnancy is confirmed and the abdomen or pelvis needs imaging, the practitioner re-justifies the exposure and considers ultrasound or MRI.

6. Children, shielding and staff protection

Children

Use paediatric protocols, collimate tightly, immobilise appropriately to avoid repeats, and avoid routine comparison views of the uninjured side. Always ask whether an X-ray will change management: many minor paediatric injuries are diagnosed and treated clinically.

Patient shielding

Lead (or lead-equivalent) shielding of patients' gonads and other organs was routine for decades. UK professional bodies, led by guidance from the British Institute of Radiology in 2020, and US bodies have since moved away from routine patient shielding for most diagnostic X-ray examinations. The reasons include the very low doses from modern equipment, shields that slip into the field of view (hiding anatomy or triggering automatic exposure control to increase the dose), and repeat exposures. Departments may still use shielding in specific situations, and patients who ask for it should have the reasons explained. Follow your local policy.

Staff protection

For staff, the classic principles are time, distance and shielding: minimise time near the beam, stand back (dose falls rapidly with distance, roughly with the square of the distance from the source), and use lead aprons, mobile screens and thyroid shields during fluoroscopy and mobile radiography. During ward films, move away from the patient when the radiographer asks. Staff are covered by separate regulations (IRR17) with occupational dose limits and monitoring.

7. Talking to patients about risk

• Use background comparisons: "A chest X-ray is about the same as two or three days of the natural radiation we all receive."
• Acknowledge the question as reasonable, and explain why the test is needed and what it will change.
• Avoid false certainty in either direction: neither "there is no risk" nor exaggerated warnings.
• For CT, it is reasonable to say the dose is higher and that the benefit has been weighed against it.

8. Common pitfalls

• Requesting "just in case". Every exposure needs a clinical question.
• Repeating recent imaging without checking PACS for what has already been done.
• Withholding a needed test from a pregnant patient out of misplaced caution, when the fetal dose is negligible.
• Equating "low dose" with "no dose", especially in children and those having frequent imaging.
• Insisting on shielding that may obscure the area of interest and lead to a repeat.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Rough doses for a chest film, an abdominal film and CT; justification versus optimisation; the duty holder roles.
Nurse	Pregnancy questions, explaining dose to worried patients, and staff protection during mobile films.
Junior doctor	Write requests that can be justified, use iRefer, and choose ultrasound or MRI when they answer the question.
Radiographer	IR(ME)R operator duties, Pause and Check, exposure optimisation, dose indicators and local shielding policy.
Advanced / FRCR	Practitioner justification, diagnostic reference levels, and dose optimisation in CT and paediatrics.

Background: how X-ray images are made. Terms are in the glossary.

Test your foundations →

References

1. The Ionising Radiation (Medical Exposure) Regulations 2017. legislation.gov.uk
2. UK Health Security Agency. Patient dose information: guidance. gov.uk
3. Royal College of Radiologists. iRefer: making the best use of clinical radiology. irefer.org.uk
4. Society of Radiographers. Pause and Check (with the RCR). sor.org
5. British Institute of Radiology. Guidance on using shielding on patients for diagnostic radiology applications (2020). bir.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.