Radiation Biology

Unit 12

What is ionization

results when x-rays strike patients tissue

How is ionization produced

through the photoelectric effect or Compton scatter

What does ionization result in

formation of a positive atom and dislodged negative electron 

What happens when the electrons interact with other atoms within the absorbing tissue

it causes chemical changes within the cell that results in biologic damage 

How does cell damage occur

primarily through formation of free radicals 

When are free radicals formed

when an x-ray photon ionizes water

What is Free Radical

an uncharged atom or molecule that exists with a single, unpaired electrons in its outermost shell

high reactive and unstable

Damage to living tissue caused by exposure to ionizing radiation may result from what

a direct hit and absorption of an x-ray photon within a cell and absorption of an x-ray photon by water within a cell accompanied by free radicals formation 

What are the two theories to describe how radiation damages biologic tissue

Direct theory and Indirect theory

What is the Direct Theory

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

infrequent

What is the Indirect Theory

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

What happens when x-ray photons are absorbed by water within a cell

free radicals formation results and they combine to form toxins that damage cells

What is a dose-response curve

the curve is used to correlate the damage of tissue with the dose of radiation received

What is a linear relationship

the linear relationship indicated that the response of the tissues is directly proportional to the dose 

What is a non-threshold dose-response curve

suggests that no matter how small the amount of radiation received, some biologic damage occurs

What are stochastic effects

a direct function of the dose

no dose threshold; effects do not depend on the magnitude of the absorbed dose

example: cancer

Nonstochastic (deterministic) effects

somatic effects that have a threshold; effects increase in severity with increasing absorbed does

Example: loss of hair, decreased fertility 

What is the sequence of radiation injury

latent period

period of injury

recovery period

cumulative effects

What is the latent period

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

depends on the total dose of radiation received and the amount of time it took to receive dose

What is the period of injury

a variety of cellular injuries may result 

What is the recovery period

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

What is the cumulative effects

effects of radiation exposure are additive

unrepaired damage accumulates in tissues

What are determining factors of radiation injury

total dose

dose rate

amount of tissue irradiated

cell sensitivity

age 

What are short term effects

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

acute radiation syndrome ARS

What is a cute radiation syndrome

nausea, vomiting, diarrhea, hair loss, hemorrhage

What are Long-term effects 

small doses absorbed repeatedly over a long period of time

effects seen years, decade, or generations 

can cause cancer, birth abnormalities, genetic defects

What are somatic cells

all cells in the body except the reproductive cells

seen in the person irradiated not in future generations

What are genetic cells

the reproductive cells

not seen in the person irradiated, but passed on to future generations

What effects of radiation can be classified as somatic or genetic 

biologic effects 

What is radiosensitive

a cell that is sensitive to radiation

What is radioresistant

a cell that is resistant to radiation

What is the response determined by

mitotic activity, cell differentiation, and cell metabolism 

What are radiosensitive organs

lymphoid tissue

bone marrow

testes

intestines

What are radioresistant tissues

salivary glands

kidney

liver

What is a critical organ

an organ that if damaged, diminishes the quality of a persons life 

What are the critical organs exposed during dental radiographic procedures

skin

thyroid gland

lens of the eye

bone marrow

What are units of measurements used in traditional units of radiation

roentgen (R)

radiation absorbed does (rad)

roentgen equivalent (in) man (REM)

What are the units of measurement in SI or newer units of radiation

coulombs/kilograms (C/kg)

gray (gy)
sievert (Sv)

What is the Roentgen unit measurement

an exposure measurement that measures radiation by determining the amount of ionization that occurs in air, NOT the amount of radiation absorbed

In SI units how is exposure stated

in coulombs per kilogram

What is the Rad or radiation absorbed dose measurement 

the amount of energy absorbed by tissue 

What is the SI equivalent to Rad

gray

1Gy=100 Rads

What is the REM or roentgen equivalent man measurement

the dose equivalent measurement is used to compare biologic effects of different kind of radiation

What is the SI equivalent to REM 

sievert

1Sv=100 REMs 

What is used to express the small doses used in dental imaging

Milli meaning 1/1000

What is natural background radiation

a form of ionizing radiation that is ubiquitous in the environment

What is cosmic radiation 

stars and sun

What is terrestrial radiation

radioactive materials in the earth and air

What is the average dose of background radiation received by an individual in the US per year

150 to 300 mrads