Radiation Health and Safety
Dose, Units, and ALARA
Every exposure should follow ALARA - as low as reasonably achievable. Know the unit conversions: 1 rad = 0.01 Gy; 1 rem = 0.01 Sv; 1 roentgen = 2.58 × 10⁻⁴ C/kg. Radiation effects are cumulative, and current theory holds that there is no threshold dose below which exposure is risk-free.
Filtration, Collimation, and Distance
Inherent filtration (0.5–1.0 mm Al equivalent) plus added filtration should total at least 2.5 mm Al for machines operating above 70 kVp. Collimate to the smallest field; rectangular collimation significantly lowers patient dose compared with a round 2.75-inch PID. A long 16-inch PID reduces skin dose to roughly one-quarter that of an 8-inch PID, per the inverse square law.
Technique and Operator Protection
kVp governs beam quality (penetration and contrast); mA and exposure time govern quantity (density). F-speed film is the fastest conventional intraoral film, and digital sensors typically reduce dose by 50–90%. Use a lead apron of 0.25 mm Pb equivalent plus a thyroid collar. The operator stands at least 6 feet from the tube head, at a 90–135° angle to the primary beam, behind a barrier - and never holds the PID or a film in a patient’s mouth.
Traps
Questions swap kVp with mA, or suggest steadying the PID by hand for a child. Others confuse the operator’s safe distance with the recommended distance to the receptor.
Worked Example
Moving from 8 inches to 16 inches: intensity becomes (8/16)² = 1/4. Rule of thumb: inverse square law - double the distance, quarter the dose.