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Effects of Radiation
It is very important that you understand how x rays and the radiation produced by them effect living organisms, especially you and your patient. There are three ways x-rays interact with organic matter: Classical Scattering, the Compton Effect, and the Photoelectric Effect.
A photon may come into contact with an atom and interact with an electron. If the photon does not have enough energy to actually displace the electron from the atom it gives its energy to the electron. The electron then produces another photon with the same energy as the other and sends it off in a different direction. This is called Classical Scattering.
If the photon has enough energy it will displace the electron from its orbit around the atom. The electron, called a recoil electron, is lost from the atom. The atom absorbs the energy from the photon, but is now missing one electron. This atom will now have a net positive charge and is called an ion. This is called the Photoelectric Effect.
If the photon collides with an atom and has enough energy to displace it, but does not transfer all of its own energy to the atom or the electron, it will continue on weaker as scattered radiation. This is called the Compton Effect.
These three reactions in themselves are not life threatening. The molecular interactions of these altered atoms can result in breaking molecules into smaller pieces, disrupting molecular bonds, and forming new bonds within or between molecules. Radiation can also interact with the water or oxygen in cells to disturb their delicate balance and damage DNA molecules.
High doses of radiation to the entire body can cause acute effects. Long term or chronic effects come from repeated exposure to radiation. The body attempts to repair the damage but cannot keep up if the exposures are regular enough or strong enough.
Operators of x-ray devices should monitor the amount or radiation they are exposed to by using a film badge. These badges are worn while at work and then sent in to a company at regular times to be evaluated for radiation exposure. Operators should step behind a lead barrier when exposing films. If no barrier is available, stand at least 6 feet away and between 90 and 135 degrees to the primary beam. Operators should never hold the film for a patient during exposure.
Radiographs should not be taken unless the benefit for the patient outweighs the risk of the radiation exposure. This is the main reason for using an excellent technique in radiology: less retakes means less exposure. Lead aprons must be used on all patients, and a thyroid collar during intraoral films.
Radiation exposure varies according to the film speed, the technique used, the kilovoltage used, and the amount of collimation used. The paralleling technique using a "long cone" provides the least amount of radiation and the best quality radiograph. Rectangular collimation reduces the area of tissue exposed to the x-ray beam by 60 to 70%.
The fastest film, at least speed "D" film, should be used for bitewings and periapicals. The clinician should also use the least number of films possible that will accurately represent the area in question.
An x-ray beam with the lowest possible kilovoltage should be used, at least 60 kVp. Filtration equivalent to 2.5 mm of aluminum should be used for 70 kVp or more. Those units operating below 70 kVp should have the equivalent of 1.5 mm of aluminum.
A patient would have to have 25 complete mouth series in a short time to significantly increase his or her risk of skin cancer. The benefit of detecting disease that may not be otherwise detected far outweighs the risk of radiation in the small doses used for dental radiography.
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