Ch. 3: Radiation Biology

total transfer of energy from x-ray photon to patient tissue

absorption

mechanisms of radiation injury

ionization

free radical formation

formation of positive atom and dislodges negative electron; occurs when x-ray photon hits tissues

ionization

x-ray photon ionizes water in cells

free radical formation

Steps of free radical formation

1. x-ray photons interact with water in cells

2. ionization occurs

3. free radicals combine

4. toxins produced

ionizing radiation directly hits critical targets within cells; occurs infrequently

direct theory of radiation

radiation causes chemical damage to cells by ionizing the water within it; occurs frequently

indirect theory of radiation injury

correlates dose of radiation administered with response or damage to tissues

dose response curve

response of the tissues is directly proportional to the dose

linear dose response curve

small amounts of radiation would not cause biological damage; not believed to be true

threshold dose response curve

no matter how small the amount of radiation recieved, some biological damage occurs 

nonthreshold dose response curve

low levels of radiation exposure ____ usually produce an observable adverse biological effect.

don’t

biological response is based on the probability of occurrence rather than the severity of the change; do not have a dose threshold

stochastic effect

severity of the change is dependent on the dose; require larger dose than stochastic effect

nonstochastic effect

Sequence of radiation injury

latent period

period of injury

recovery period

time that elapses between exposure to ionizing radiation and the development of the biological effect

latent period

What does the latent period depend on?

total dose of radiation and rate or amount of time dose was recieved

occurs after the latent period when effets can be observed

period of injury

not all celluar radiation injuries are permanent and the body can recover

recovery period

effects of radiation exposure are additive and unrepaired damage can accumulate in tissues

cumulative effects

What are factors that influence degree of radiation injury?

total dose

dose rate

amount of tissue irradiated

age

cell sensitivity 

quantity of radiation received

total dose

rate at which radiation exposure occurs

dose rate

Total body radiation produces ____ adverse effects than if a small, localized area of the body is exposed

more

What age group is more susceptible to radiation?

children

more damage occurs in cell that are more sensitive to radiation

cell sensitivity

Short term radiation is seen within…

minutes, days, or weeks after the latent period

Long term radiation effects are seen…

years, decade, and generation after the latent period

effects seen in the person irradiated, not transmitted to future generations

somatic effects

produces changes in genetic cells effecting the health of future generations but NOT the exposed individual

genetic effects

cell is sensitive to radiation

radiosensitive

cell is resistant to radiation

radioresistant

Law of B and T

The greater the proliferation rate of cells and the growth rate for tissues, the greater the radiosensitivity

The younger the tissues and organs are, the ______ the radiosensitivity.

greater

The more mature a cell is, the ____ resistant it is to radiation.

more

The higher the metabolic activity of a cell is, the ______ the cell’s radiosensitivity.

higher

The more differentiated (specialized in function), the ____ resistant it is to radiation.

more

radiosensitive cells

Lymphocytes

Bone marrow

Reproductive cells

Immature bone

Intestinal mucosa

Skin

Lens of eye

Oral mucosa

radioresistant cells

Mature bone

Muscle

Nerve

Salivary gland

Thyroid gland

Kidney

Liver

What are critical organs in dentistry?

skin, thyroid gland, lens of eye, and bone marrow

What is radiation measured in?

time, distance, and weight

amount of energy or ionizing radiation produced by x-ray machine

exposure measurement

amount of energy absorbed by tissue at a specific point

absorbed dose

absorbed dose X a biological-effect qualifying or weighting factor

used to facilitate comparison of biological effects of various types of radiation

dose equivalent

puts different types of radiation on a common scale so they can be compared

QF for x-rays = 1

qualifying factor 

taditional system exposure unit

Roentgen (R)

SI exposure unti

Coulumb/kilogram (C/kg)

traditional system absorbed dose unit

Rad (radiation absorbed dose)

SI absorbed dose unit

Gray (Gy)

1 Gy =  ___ rads

100

1 rad = ___ Gy

.01

traditional system dose equivalent unit

rem (roentgen equivalent in man)

SI dose equivalent unit

Sievert (Sv)

1 Sv = ___ rems

100

1 rem = ___ Sv

.01

effective dose equivalent 

used to compare the risk of the radiation exposure producing a

biological response

compensates for the difference in area exposed and the tissues

(critical or less critical) that may be in the path of the x-ray beam

effective dose equivalent unit

mSv

likelihood of adverse effects or death resulting from exposure to a hazard

risk

chance of cancer from dental radiographs

3 in 1 million

chance of spontaneous development of cancer

3300 in 1 million

chance of fatal outcome

1 in 1 million