Sources of radiation
There are three sources of radiation in the dental office, primary, secondary and leakage. Primary and leakage radiation emanate from the x-ray machine. Primary radiation is generated at the anode target, collimated by the PID and directed toward patient to produce radiographs. Secondary radiation is scatter radiation created by primary beam interaction with matter such as the patient’s face and oral structures. And leakage, a form of secondary radiation, is emitted from the tube head encasement when x-rays are generated inside the x-ray tube. The dental assistant should avoid all three sources to minimize occupational exposure.
Maximum permissible dose and maximum accumulated dose
Individuals who use radiation to carry out their professional responsibilities are classified as occupationally exposed persons. Dose limits have been established for occupationally exposed persons, non-occupationally exposed persons (general public) and occupationally exposed pregnant women. The maximum permissible dose (MPD) is the dose of whole body radiation that is not expected to produce any significant somatic or genetic effects in a lifetime. Table 4 outlines the MPD for all three categories in both traditional and SI units and well as a formula for calculating the maximum accumulated dose for occupationally exposed persons. MPD compliance is achieved through adherence to radiation safety practices. The dental assistant’s ultimate goal should be zero occupational exposure.
|Table 4. Maximum Permissible Dose|
|MPD Dose Limits||Traditional Units||SI Units||Cumulative Dose|
|Radiation worker||5.0 rem/year||50 mSv/year||10 mSv X age|
|Pregnant radiation worker||0.5 rem term||5 mSv term|| |
|General public||0.1 rem/year||1 mSv/year|| |