Radiation Biology

Radiation Biology

The study of the effects of ionizing radiation on living tissue and to understand the harmful effects of x-radiation.

Ionization - Free Radical Formation

2 Specific mechanisms of radiation injury.

Ionization

Produced through the photoelectric effect or Compton scatter and results in the formation of a positive atom and dislodged negative electron.

Free Radical

Occurs when an x-ray photon ionizes water.

Free Radical

An uncharged neutral atom or molecule that exists with a single unpaired electron in the outermost shell; highly reactive and unstable.

Direct Theory

Suggest that cell damage results when ionizing radiation directly hits critical areas/target from the cell.

Indirect Theory

Suggest that x-ray photons are absorbed within the cell and cause the formation of toxins which in turn damage the cell.

Stochastic Effects

Occur as direct function of dose; the probability of occurrence increases with increasing absorbed dose.

Nonstochastic Effects

Are somatic (deterministic) effects that have a threshold and increase in severity with increasing absorbed dose.

Latent Period

Can be defined as the time that elapses between exposure to ionizing radiation and the appearance of observable clinical sign.

Shorter

The more radiation received and the faster the dose rate, the _______ the latent period.

Total Dose

Refers to the quantity of radiation received or the total amount of radiation energy absorbed; more damage occurs when large quantities of radiation are absorbed by a tissue.

Dose Rate

Rate at which exposure to radiation occurs and absorption takes place; dose rate= dose/time.

Amount of Tissues Irradiated

Refers to the areas of the body exposed.

Somatic Effects

Are seen in the person irradiated; radiation injuries that produce changes in somatic cells (all cells in the body except the reproductive cells).

Radiosensitive

Cells that are sensitive to n.

Radioresistant

Cells that are resistant to radiation.

E

Film of a speed slower than _-speed should not be used for dental radiograph.

Intensifying Screens

Screens which absorb the energy in the x-ray beam that has penetrated the patient and convert this energy into a light pattern which has as nearly as possible the same information as the original x-ray beam.

Rare Earth Screens

These screens decrease patient exposure by as much as 55% in panoramic and cephalometric radiography.

Rectangular Collimator

Decreases the radiation dose by up to fivefold as compared with a circular one, radiographic equipment should provide rectangular collimation for exposure of periapical and bitewing radiograph.

Filtration

To remove low energy x-ray photons which will decreased patient exposure with no loss of radiographic information.

Lead Aprons and Collars

Reduced radiation exposure of the gonads and thyroid gland.

Film and Sensor Holders

Improve the alignment of the film with teeth and xray machine. Results in a significant reduction in unaceptable images.

50 - 100

Kilovoltage must range between __ and ___ kilovolt peak but should range between 60-80 kVp.

Milliampere-seconds

Set the amperage and time settings for exposure at an optimal quality.