Ch 3 Radiation Biology

T or F- all ionizing radiation are harmful and produce biological changes in living tissues

True

What are two ways ionization injury can occur?

1. Ionization

2. free radical formation

How does injury occur from ionization?

The ejected electron in absorption or Compton scatter interacts with other atoms resulting in further ionization, excitation, or breaking of molecular bonds all which cause chemical changes in the cell that may result in biological damage

How does free radical formation occur?

When an x-ray photon ionizes water, the primary component of living cells.

what is a free radical?

An uncharged atom that is unstable and highly reactive because it contains unpaired electrons

How do free radicals try to achieve stability?

1. recombine without causing changes in molecule

2.combine with other free radicals and cause changes

3. Combine with ordinary molecules to form a toxin (hydrogen peroxide) capable of producing widespread cellular changes

Direct theory of radiation injury

cell damage results when ionizing radiation directly hits critical areas within the cell such as DNA- infrequent

what happens to most x-ray photons as they reach matter?

they pass through the cell and cause little or no damage

indirect theory of radiation injury

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

Why does indirect injuries of radiation occur frequently

the cell is 70 to 80 percent water

dose response curve

a graph used to correlate the response or damage of tissues in relation to the amount of radiation received

Linear curve

response of the tissues is directly proportional to the dose

Linear nonthreshold

no matter how small the amount of radiation, some biological damage occurs - threshold dose level does not exist

Threshold Dose

below a certain threshold, no response of injury is seen

Stochastic effects

direct function of dose with the probablility of occurrence increasing with increased dose, ex. cancer, genetic mutations

do stochastic effects have a threshold

no

T or F- for stochastic effects the severity of effects does not depend on the magnitude of the absorbed does

true

Nonstochastic effects

have a threshold and increased severity with increased absorbed dose, ex. loss of hair, decreased fertility, erythema

Non stochastic effects occur when?

threshold level has been reached

list the sequence of radiation injury

latent period

period of injury

recovery period

cumulative effects

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

shorter

what are determining factors for radiation injury?

1. Total dose

2. Dose rate

3. Amount of tissue irradiated

4. Cell sensitivity

5. Age

which cells are more sensitive to radiation?

rapidly dividing cells and young cells

short term effects

large amounts of radiation absorbed in a short time - effects seen within minutes

examples of short term effects of radiation

ARS- vomiting, nausea, diarrhea, hair loss, hemorrhage

Long term effects

small amounts of radiation absorbed repeatedly over a long period

examples of long term effects

birth defects genetic defects, cancer

somatic vs genetic cells

somatic - all cells in the body expect for reproduction

genetic- reproductive cells

Somatic effects

Effects of radiation that cause illness and are responsible for poor health (such as cancer, leukemia, and cataracts) but are not passed on to offspring.

genetic effects

Not seen in the person irradiated

Passed on to future generations

T or F- genetic damage can be repaired

false

the cell...... is more sensitive to radiation than the cytoplasm

nucleus

radiosensitive vs radioresistance

cells that are sensitive to radiation vs cells that is resistant

The response of a cell to radiation exposure is determined by:

miotic activity (divisions), cell differentiation, cell metabolism

Radiosensitive cells examples

blood, cells, immature reproductive cells, and young bone cells

the cell that is most sensitive to radiation

small lymphocyte

Radioresistance cells example

bone, muscle, and nerve cells

radiosensitive organs

bone marrow, intentional mucosa, skin, lens of eyes, oral mucosa, testes

radioresistant organs -

salivary glands, kidneys, liver, mature bone and tissue, thyroid gland

critical organs that is exposed during dental imaging

thyroid gland

bone marrow

skin

lens of eyes

What does Roentgen measure?

amount of ionization in the air

what is the limitation of roentgen

It does not describe the amount of radiation absorbed, only the amount of energy that reaches the surface of an organism

roentgen is used only for what electromagnetic radation

x-rays and gamma rays

No SI unit is equivalent to R instead......

stated in coulombs per kilograms (C/kg)

Coulombs measures what

unit of electrical charge (number of ion pairs)

Dose

the amount of radiation absorbed by a tissue

T or F- RaD can be applied to all forms of radiation

True

what does RaD measure?

Amount of energy absorbed in any medium- does not take into account of the sensitivity of cells

what is the SI equivalent of Rad

Gray (Gy)

what does the dose equivalent measure

Roentgen equivalent in man (Rem)

compare the biological effects of different tissues on radiation

SI equivalent for REM

Sievert (Sv)

is rem or Sv preferred ?

SV

what is unique about rem

it uses a quality factor- not all radiation produce the same effects

The Sv not only accounts for absorbed dose in soft tissues but also takes into consider the radiosensitivity of certain tissues

Natural or background radiation

have always been a part of the human environment since the formation of the universe.

examples of background radiation

Radon in the air, thorium in earth, cosmic rays, radioactive potassium in food, radioactive material in human body,

what is the single greatest source of exposure to background radiation in the US

radon gas from soil

In the US the average person is exposed to how much radiation per year

3.1 mSv

how much is the average person exposed to manmade radiation per year

3.1 mSv

what is the greatest source of man made radiation exposure

medical radiation

examples of man made radiation

consumer products- tv computer

fallout from atomic weapons

weapons production'

nuclear fuel cycle

required dose to cause cancer in thyroid gland

6,000 mrad

0.06 Gy

required dose to cause leukemia in bone marrow

5,000 mrad

0.05 Gy

required dosage to cause skin erythema

250 rad (2.5 Gy) in a 14 day period - more than 500 dental films

required dose to cause cataract

200,000 mrad

2 Gy

how can patient exposure be reduced?

receptor choice - digital imaging or f speed fiilm

collimation- reduce amount of radiation

technique - increasing target receptor distance

dental imaging should only be prescribed when?

when the benefit of disease detection outweighs the risk of biological damages.