Radiation protection principles

Practical approach in theatre/ICU (fluoroscopy, mobile C-arm, IR, CT transfer)

Before the case: confirm justification and planning
- Ensure imaging is clinically necessary; consider alternatives (US, MRI) where appropriate
- Identify high-dose scenarios: prolonged screening, obese patient, steep angulations, complex endovascular/orthopaedic cases
During fluoroscopy: apply ALARP using time, distance, shielding
- Time: use pulsed fluoro, last-image hold, minimise magnification, collimate tightly, avoid unnecessary cine runs
- Distance: step back during screening; inverse square law applies to point sources (approximation for scatter)
- Shielding: wear correctly fitted lead apron (typically 0.35–0.5 mm Pb eq), thyroid collar; use ceiling-suspended screens and table skirts
Positioning relative to C-arm: reduce scatter exposure
- Scatter is greatest on the X-ray tube side; stand on the image intensifier/detector side where possible
- Keep hands out of beam; never hold patient in beam—use positioning aids
Pregnancy: staff and patient considerations
- Staff: declare pregnancy early to enable risk assessment and appropriate monitoring; aim to keep fetal dose very low (workplace controls, shielding, distance)
- Patient: justify and optimise; consider gestation; use shielding where it does not interfere with imaging; document counselling when relevant
After the case: documentation and follow-up for high-dose procedures
- If significant skin dose suspected (prolonged fluoro/cine): ensure local pathway for patient advice and skin injury follow-up
- Report and investigate unusual exposures/near misses via local radiation protection processes

Core principles and terminology

Goal: maximise clinical benefit while minimising harm from ionising radiation
Three fundamental protection principles (ICRP): justification, optimisation (ALARA/ALARP), dose limitation (for workers/public; not for patients undergoing justified medical exposure)
ALARP/ALARA: reduce dose to as low as reasonably practicable/achievable, considering economic and societal factors
Deterministic (tissue reactions): threshold dose; severity increases with dose (e.g., skin erythema, cataract). Stochastic: no threshold; probability increases with dose (cancer, heritable effects)

Dose quantities used in protection (definitions you can say in a viva)

Absorbed dose (gray, Gy): energy deposited per unit mass (J/kg)
Equivalent dose (sievert, Sv): absorbed dose × radiation weighting factor (wR). For X-rays and gamma, wR = 1
Effective dose (Sv): sum of equivalent doses to organs × tissue weighting factors (wT); reflects whole-body stochastic risk
Personal dose equivalent: Hp(10) approximates effective dose (deep dose); Hp(0.07) for skin/extremity; Hp(3) for lens
Operational fluoroscopy metrics: KAP/DAP (Gy·cm²) correlates with stochastic risk; cumulative air kerma at reference point (Ka,r, Gy) correlates with skin injury risk

How to reduce dose in fluoroscopy (patient and staff)

Time: reduce screening time; use pulsed fluoroscopy and lowest acceptable frame rate; avoid unnecessary cine; use last-image hold
Distance: inverse square law (dose ∝ 1/r²) for point source; for staff exposure mainly from scatter—distance still markedly reduces dose
Shielding: lead apron, thyroid collar, lead glasses; ceiling-suspended lead acrylic screen; table-side curtains; mobile shields
Beam geometry: collimate; keep detector close to patient; keep X-ray tube as far from patient as practical; avoid steep obliques when possible
Magnification and image quality: magnification increases dose; use only when necessary; accept slightly noisier images if clinically adequate
Patient factors: increased thickness increases dose (automatic exposure control raises tube output); anticipate higher dose in obesity and plan protection accordingly

Shielding and PPE (what to know and say)

Lead aprons: typically 0.35–0.5 mm Pb equivalent; reduce scatter to trunk substantially but not to zero; ensure correct fit and overlap (wrap-around for those turning)
Thyroid collar: important due to radiosensitivity of thyroid and proximity to scatter field
Lead glasses: reduce lens dose; particularly relevant with prolonged fluoroscopy and when close to patient
Gloves: leaded gloves provide limited protection and can increase dose if placed in beam (automatic exposure increases output); best strategy is keep hands out of beam
Apron care: hang (do not fold), inspect for cracks, replace when damaged; ensure local QA programme

Legislation and roles (UK-focused)

IRR17 (Ionising Radiations Regulations 2017): protects workers/public from occupational exposure; requires risk assessment, local rules, controlled/supervised areas, training, monitoring, dose limits
IR(ME)R 2017 (Ionising Radiation (Medical Exposure) Regulations): protects patients; requires justification, optimisation, diagnostic reference levels (DRLs), defined duty holders
Duty holders under IR(ME)R: referrer (requests), practitioner (justifies), operator (carries out practical aspects). Individuals can hold more than one role if entitled/trained
RPA (Radiation Protection Adviser): advises employer on IRR17 compliance. RPS (Radiation Protection Supervisor): ensures adherence to local rules in department/area
MPE (Medical Physics Expert): involved in optimisation, dosimetry, QA and patient dose matters under IR(ME)R

Dose limits and monitoring (numbers to learn)

Occupational effective dose limit: 20 mSv/year (averaged over defined periods in regulation; practically treated as 20 mSv per year limit)
Lens of the eye limit (occupational): 20 mSv/year (reflects updated lower threshold for cataract)
Skin limit (occupational): 500 mSv/year (averaged over 1 cm²); extremities also 500 mSv/year
Public effective dose limit: 1 mSv/year
Pregnant worker: after declaration, apply additional controls so fetal dose is unlikely to exceed 1 mSv for remainder of pregnancy (commonly used constraint in UK practice)
Monitoring: personal dosimeters (e.g., TLD/OSL). If wearing apron: wear at collar outside apron for lens/thyroid estimation; some workplaces use a second dosimeter under apron to estimate effective dose
Controlled areas: designated where special procedures needed to restrict exposure; local rules specify entry, PPE, and monitoring requirements

Patient protection concepts (IR(ME)R)

No formal dose limits for patients undergoing justified medical exposure; instead: justification, optimisation, DRLs, and recording/reporting of significant accidental/unintended exposures
DRLs: typical dose levels for standard procedures; exceeding DRL prompts review of technique/equipment/patient factors (not an absolute maximum)
High-dose interventional procedures: monitor Ka,r and KAP/DAP; consider skin dose mapping and follow-up if thresholds approached/exceeded

Explain the three fundamental principles of radiation protection and how they apply to an anaesthetist in a fluoroscopy list.

Structure your answer as: justification → optimisation (ALARP) → dose limitation (staff/public).

Justification: only perform exposures that are clinically indicated; consider non-ionising alternatives (US/MRI) and avoid repeat imaging
Optimisation (ALARP): minimise dose for required image quality using time–distance–shielding, collimation, pulsed fluoro, last-image hold, avoid magnification
Dose limitation: applies to occupational/public exposures; comply with dose limits, wear dosimeter, follow local rules and use shielding

Define absorbed dose, equivalent dose and effective dose. Why do we use sieverts?

Examiners want clear definitions and what each quantity represents.

Absorbed dose (Gy): energy deposited per unit mass (J/kg) in a material/tissue
Equivalent dose (Sv): absorbed dose × radiation weighting factor (wR); accounts for different biological effectiveness of radiation types (X-rays: wR=1)
Effective dose (Sv): sum of organ equivalent doses × tissue weighting factors (wT); estimates whole-body stochastic risk
Sievert is used for protection quantities because it relates dose to biological risk (stochastic effects) rather than just physical energy deposition

A C-arm is used for a hip fracture. Where should you stand to minimise your dose and why?

Key concept: staff dose is mainly from scatter off the patient; geometry matters.

Stand on the detector/image intensifier side rather than the X-ray tube side because scatter is greater on the tube side
Maximise distance from the patient during screening; even a step back can significantly reduce scatter exposure
Use ceiling-suspended screen/table skirts if available; keep hands out of the beam

What practical steps reduce patient dose during fluoroscopy, and how do they also reduce staff dose?

Patient dose reduction usually reduces scatter and therefore staff dose.

Collimation reduces irradiated volume → reduces patient dose and scatter to staff
Pulsed fluoroscopy / lower frame rate and minimise screening time reduce total dose and scatter
Avoid magnification unless necessary; keep detector close to patient to improve efficiency and reduce required output
Avoid steep oblique angles where possible; they increase path length through tissue and increase tube output

What are the UK occupational dose limits relevant to an anaesthetist and what do they mean in practice?

Know the headline numbers and which tissues they apply to.

Effective dose: 20 mSv per year (occupational limit)
Lens of eye: 20 mSv per year (occupational limit)
Skin and extremities: 500 mSv per year
In practice: comply with local rules, wear dosimeter correctly, use shielding; investigate if doses trend upwards or approach investigation levels

Where do you wear your dosimeter when wearing a lead apron, and why might you need two?

Answer depends on local policy; give the rationale.

Common approach: wear dosimeter at collar outside apron to estimate dose to head/neck (including lens) and to monitor scatter field
Two-dosimeter method: one under apron at chest/waist to estimate effective whole-body dose, plus one at collar for lens/thyroid region
Extremity monitoring (ring badge) may be used for operators with hands close to beam (e.g., interventionalists)

What is the difference between IRR17 and IR(ME)R 2017, and which applies to you in theatre?

Frame it as: workers/public vs patients; and duty holders.

IRR17: occupational/public exposure; employer duties include risk assessment, controlled areas, local rules, training, monitoring, dose limits
IR(ME)R 2017: medical exposures to patients; requires justification, optimisation, DRLs, QA; defines referrer/practitioner/operator roles
In theatre: you are a worker under IRR17; you may also be an IR(ME)R operator for aspects you perform (e.g., assisting positioning, following instructions) depending on local entitlement/training

Define deterministic and stochastic radiation effects. Give examples relevant to staff and patients.

Include threshold concept and how risk scales.

Deterministic (tissue reactions): threshold dose; severity increases with dose. Examples: skin erythema/burns after prolonged fluoroscopy (patient), cataract (staff/patient)
Stochastic: no threshold; probability increases with dose. Examples: radiation-induced cancer risk from CT/fluoroscopy (patient) and occupational exposure (staff)

What is DAP/KAP and why is it useful? What does cumulative air kerma tell you?

These are commonly displayed on modern fluoroscopy systems and appear in incident reviews.

DAP/KAP (Gy·cm²): dose × beam area; correlates with total energy delivered and is used as a surrogate for stochastic risk and for comparing technique between cases
Cumulative air kerma at reference point (Ka,r, Gy): correlates with peak skin dose and deterministic skin injury risk in interventional procedures

A pregnant anaesthetist is rostered to an interventional radiology list. What are the key radiation protection steps?

Focus on declaration, risk assessment, monitoring, and practical dose reduction.

Encourage early declaration of pregnancy to trigger formal risk assessment and workplace controls
Aim to keep fetal dose very low; commonly used constraint is that fetal dose should be unlikely to exceed 1 mSv for the remainder of pregnancy
Use strict time–distance–shielding: maximise distance during screening, use ceiling/table shields, wear properly fitted wrap-around apron and thyroid collar; consider additional monitoring per local policy
If unable to control exposure adequately for a particular list, adjust duties/rota in line with occupational health and local rules

Why can lead gloves be counterproductive in fluoroscopy?

This is a common viva trap: gloves are not a licence to put hands in the beam.

If a gloved hand enters the primary beam, automatic exposure control may increase tube output to maintain image brightness, increasing dose to patient and potentially to the hand
Leaded gloves attenuate less than aprons and are mainly for scatter; best practice is to keep hands out of the primary beam

What are controlled and supervised areas, and what does it mean for your behaviour in theatre?

Relate to IRR17 and local rules.

Controlled area: area where special procedures are needed to restrict significant exposure; entry may require authorisation, PPE, and compliance with local rules
Supervised area: lower risk; conditions are kept under review but may not need the same level of controls as controlled areas
In theatre with C-arm: treat as controlled during exposures—wear PPE, stand back/behind shields, minimise personnel present, and follow RPS/local rules