The principle of ALARA in radiation protection stands for 'As Low As Reasonably Achievable.' The three basic principles of external radiation protection to minimize dose are:

• A Filtration, collimation, and scatter reduction
• B Distance, shielding, and time ✓
• C Beam energy, field size, and grid use
• D Justification, optimization, and dose limits

Explanation

The three cardinal principles of external radiation protection are: (1) Distance — radiation intensity decreases with the square of the distance from the source (inverse square law), so doubling the distance reduces dose to one-quarter; (2) Shielding — interposing absorbing material (lead, concrete) attenuates the beam; (3) Time — minimizing time spent near a radiation source reduces cumulative dose proportionally. These apply to radiographers and staff working around X-ray and fluoroscopy equipment. Option D describes the ICRP system of radiological protection principles rather than practical dose minimization methods.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.