Most dose-reduction strategies follow the optimisation (ALARA) principle which states, every exposure should deliver the lowest dose reasonably achievable for the required clinical information.

This lesson touches on many different aspects of dose reduction. I’ve tried to keep it concise and focus on strategies that get asked about in exams.

Pass your radiology physics exam first time

Factors Influencing Patient Dose

Patient dose depends on:

Exposure parameters (kVp, mAs, filtration).
Field size and collimation.
Use of anti-scatter grids.
Patient size and positioning.
Equipment calibration and detector efficiency.

Technical Strategies for Dose Reduction

Parameter / Technique	Principle	Effect on Dose / Image Quality
High kVp, low mAs technique	Higher energy photons more penetrating; fewer interactions per unit dose	↓ Dose, ↓ contrast (but acceptable for most exams)
Automatic Exposure Control (AEC)	Terminates exposure once optimal detector signal achieved	Ensures consistent detector dose; prevents overexposure
Tight collimation	Restricts beam to region of interest	↓ Scatter, ↓ dose, ↑ contrast
Added filtration	Removes low-energy photons that would be absorbed superficially	↓ Skin dose, minimal effect on image quality
Remove anti-scatter grid when not required	Grids increase mAs requirement	↓ Dose in thin patients (<10 cm)
Use of high-DQE detectors	Efficient X-ray-to-signal conversion	Allows dose reduction for same SNR
Optimised SID and OID	Larger SID, smaller OID reduce skin dose and geometric blur	↓ Dose to skin and improves sharpness
Appropriate exposure charts	Standardise technique by body part and thickness	Prevents unnecessary repeats and overexposures

Repeat Exposures

Repeat imaging is a major avoidable source of radiation dose.
Common causes include:

Poor positioning or collimation.
Incorrect exposure factors.
Motion blur.
Artefacts from clothing, jewellery, or equipment.

Prevention:

Staff training and standardised protocols.
Quality control (QC) checks.
Immediate image review to detect positioning errors before repeating series.

Special Techniques for Dose Reduction

These are factors unique to certain modalities. A little heads up, these are examiners favourites for exams!

Modality / Context	Method	Explanation / Effect
Fluoroscopy	Pulsed fluoroscopy, last-image hold	Reduces exposure time by 50–80%
Mammography	Breast compression	Reduces tissue thickness → lower mAs, ↓ scatter
CT (for completeness)	Tube current modulation, iterative reconstruction	Dose reduction up to 40–60%
Mobile radiography	Ensure detector flush with patient and aligned to tube	Minimise repeat exposures

Monitoring and Feedback

Modern X-ray units display Dose–Area Product (DAP) or Exposure Index (EI) values after each exposure.
These allow comparison with Diagnostic Reference Levels (DRLs) to ensure practice remains within acceptable limits.

DRLs: Set at the 75th percentile of national dose distributions.
Not dose limits but investigation levels. If doses are above DRL this prompts a review of technique or equipment performance.

Key Takeaways and Exam Tips:

Dose reduction follows ALARA: minimise dose, maintain diagnostic quality.
High kVp / low mAs technique is the simplest dose-saving approach.
Collimation and filtration reduce both dose and scatter..
Avoid repeats through careful positioning and QC.
Common exam question: “Describe methods to reduce patient dose in X-ray imaging and their effect on image quality.”