Radiation Characteristics and Biology

radiation biology

The study of ionizing radiation effects on living tissue and understanding harmful effects of x-rays in diagnostic radiology.

ionization

Mechanisms of Radiation Injury

• Occurs via the photoelectric effect or Compton scatter, leading to

  chemical changes that may alter DNA

free radical formation

Mechanisms of Radiation Injury

• X-ray photons ionize water, forming unstable, reactive free

  radicals that may damage cells.

direct theory

Theories of Radiation Injury

• Cell damage occurs when x-ray photons directly hit critical cell

  structures (e.g., DNA).

indirect theory

Theories of Radiation Injury

• X-ray photons are absorbed in the cell, forming toxins that cause

  damage (e.g., from ionized water).

dose

Radiation Effects

• The amount of energy absorbed by tissue

stochastic effects

Radiation Effects

• Probability increases with dose but severity is independent

  (e.g., cancer).

nonstochastic effects

Radiation Effects

• Have a threshold and increase in severity with dose (e.g.,

  tissue burns).

latent period

Radiation Injury Sequence

• Time between exposure and observable effects

period of injury

Radiation Injury Sequence

• Cell death, chromosome changes, abnormal mitosis

recovery

Radiation Injury Sequence

• Some cellular damage is repairable

cumulative effects

Radiation Injury Sequence

• Unrepaired damage accumulates (e.g., cancer, cataracts,

  birth defects).

more damage

Factors Affecting Radiation Injury

• Total dose: Higher dose = —

greater harm

Factors Affecting Radiation Injury

• Dose rate: Faster exposure = —.

young

Factors Affecting Radiation Injury

• Tissue sensitivity: Rapidly dividing and — cells are more sensitive

children

Factors Affecting Radiation Injury

• Age: — are more susceptible

short-term effects

Types of Radiation Effects

• From high-dose exposure in a short time (e.g., nuclear

  accidents).

long-term effects

Types of Radiation Effects

• From repeated low-dose exposure (e.g., genetic defects).

somatic effects

Types of Radiation Effects

• Affect the exposed individual (e.g., cancer).

genetic effects

Types of Radiation Effects

• Passed to offspring via reproductive cells

radiosensitive cells

Radiosensitivity of Cells & Tissues

• Rapidly dividing cells, younger cells

radioresistant cells

Radiosensitivity of Cells & Tissues

• Mature, non-dividing cells

time, distance, shielding

Reducing Dental Radiation Exposure

• basic control methods

monitoring exposure

Reducing Dental Radiation Exposure

• Use personal dosimeters (e.g., film badges, TLD, pocket dosimeters) to track

exposure levels

high speed film and rare earth intensifying screens

Reducing Dental Radiation Exposure

• Reduces exposure by up to 55%.

increase source-to-skin distance

Reducing Dental Radiation Exposure

• A 40 cm distance reduces exposure by 10-25%.

rectangular collimation

Reducing Dental Radiation Exposure

• Lowers dose fivefold compared to circular collimation

filtration

Reducing Dental Radiation Exposure

• Removes low-energy x-rays that do not contribute to image quality.

leaded aprons and collars

Reducing Dental Radiation Exposure

• Protect gonads and thyroid gland

film holders

Reducing Dental Radiation Exposure

• Improve alignment, reducing repeat exposures

60-80 kVp

Reducing Dental Radiation Exposure

• Kilovoltage (kVp) and Milliampere-seconds (mAs) settings should be optimized (— recommended)

overexposure, underdevelopment

Reducing Dental Radiation Exposure

• Proper Film Processing: Avoid — and — to minimize radiation dose.

6 feet (2 meters)

Personnel Protection

• Use lead barriers and maintain a — distance from the x-ray tube.

90-135

Personnel Protection

• Stand — degrees from the primary beam to reduce exposure risk