Radiology Ch.3

ionization and free radical formation

Two mechanisms of radiation injury

ionization

Results when x-rays strike patient tissue

Results in formation of a positive atom and dislodged negative electron

ionization

Dislodged electron interacts with other atoms within the absorbing tissues causing chemical changes within the cell that results in biologic damage

free radicals

formed when an x-ray photon ionizes water, the primary component of living cells

free radical

An uncharged atom or molecule that exists with a single, unpaired electron in its outermost shell

free radicals

Highly reactive and unstable

Can be dangerous because they can react with parts of the cells such as DNA

direct and indirect

Two theories to describe how radiation damages biologic tissues

direct theory

Cell damage results when ionizing radiation directly hits critical areas within the cell

Doesn’t occur frequently

indirect theory

X-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell

toxins

When x-ray photons are absorbed by water within a cell, free radical formation results. The free radicals combine to form ____ that damage cells

stochastic and nonstochastic

Two types of harmful effects of ionizing radiation

stochastic effect

direct function of the dose

No dose threshold; can occur at any dose, no minimum dose is required to have an effect

cancer and genetic mutations

What are two examples of stochastic effects

nonstochastic

Somatic effects that have a threshold; effects increase in severity with increasing absorbed dose

Requires larger radiation dose to cause serious impairment of tissue

hair loss, erythema, cataracts, decreased fertility

4 examples of nonstochastic effects

no

For nonstochastic effects, if the radiation exposure is below the threshold, will any effects occur?

yes

For nonstochastic effects, if the radiation exposure is above the threshold, will any effects occur?

latent period

The time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs

latent period

Can be short or long

Depends on the dose of radiation received and the time it took to receive the dose

period of injury

Part of the sequence of radiation injury where a variety of cellular injuries may result.

recovery period

Not all radiation injuries are permanent

Depending on a number of factors, cells can repair the damage caused by radiation

cumulative effects

Effects of radiation exposure are additive

Unrepaired damage can lead to health problems

short-term effects

Associated with large doses of radiation in a short amount of time

acute radiation syndrome

Symptoms include nausea, vomiting, diarrhea, hair loss, hemorrhage

acute radiation syndrome

What is an example of a short-term effect

long-term effects

Small doses absorbed repeatedly over a long period of time

Effects seen after years, decades, or generations

cancer, birth abnormaliites, and genetic defects

What are 3 examples of long-term effects

somatic cells

All cells in the body except the reproductive cells

genetic cells

The reproductive cells

somatic

Effects seen in the person that has been exposed to radiation

Not seen in future generations

genetic

Effects not seen in the person that has been exposed to radiation

Passed on to future generations

radiosensitive

cell that is sensitive to radiation

radioresistant

cell that is resistant to radiation

radiosensitive organs

Lymphoid tissue, bone marrow, testes, and intestines are all classified as:

radioresistant tissues

Salivary glands, kidneys, and the liver are classified as:

critical organ

An organ that, if damaged, diminishes the quality of a person’s life

skin, thyroid gland, eye lens, and bone marrow

4 Critical organs exposed during dental radiographic procedures

dose measurement

The amount of energy absorbed by tissue

dose measurement

Traditional unit for this is the rad

maximum permissible dose

the maximum dose equivalent that a body is permitted to receive in a specific period

5 rem/year

MPD for occupationally exposed persons

0.1 rem/year

MPD For nonoccupationally exposed persons

0.1 rem/year

For occupationally exposed pregnant women, MPD is

natural background radiation

A form of ionizing radiation that is found in the environment

cosmic

Radiation froms Stars and sun

terrestrial

Radiation from radioactive materials in the earth and air

150-300

In the United States the average dose of background radiation received by an individual ranges from ______ mrads per year

artificial radiation

Includes consumer products, fallout from atomic weapons, weapons production, and the nuclear fuel cycle

medical radiation

includes medical radiographic procedures, dental radiography, fluoroscopy, nuclear medicine, and radiation therapy

3

The potential risk of dental radiography inducing a fatal cancer in an individual has been estimated to be _ in 1 million

unrelated

Cancer is most likely to be ____ to radiation exposure

common activities

Death is more likely to occur from ____ _____ than from dental imaging procedures

benefit, risk

Dental radiographs should be prescribed for a patient only when the ____ of disease

detection outweighs the ___ of biologic damage