Radiation Biology

radiation biology

the study of the eects of ionizing radiation on living

tissue

Absorption

total transfer of energy from the x-ray photon to patient tissues

Two specific mechanisms of radiation injury

(1) ionization and (2) free radical formation

ionization is a production though …

photoelectric effect or Compton scatter

Two theories are used to describe how radiation damages biologic

tissues

(1) the direct theory and (2) the indirect theory

direct theory

cell damage results when ionizing radiation directly hits critical areas, or targets, within the cell.

indirect theory

x-ray photons are absorbed within the cell and cause the formation of toxins

Stochastic effects

 effect of ionizing radiation on chromosomes that result in genetic mutations

Nonstochastic effects

have a threshold and increase in severity with increased absorbed dose; only occurs after a threshold have been met

Examples of non-stochastic effects

skin erythema, loss of hair, cataract formation, decreased fertility, radiation sickness, terato-

genesis, and fetal death.

Sequence of radiation injury

latent period, period of injury, recovery period, and cumulative effects

latent period

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

period of injury

variety of cellular injuries may result, including cell death, changes in cell function, breaking or clumping of chromosomes, formation of giant cells, cessation of mitotic activity, and abnormal mitotic activity.

recovery period

cellular damage is followed by repair.

cumulative effects

additive, and unrepaired damage accumulates in the tissues

health problems from cumulative effects

cancer, cataract formation, or birth defects

Determining factors for radiation injury 

total dose, dose rate, amount of tissue irradiated, cell sensitivity, and age

Total dose

Quantity of radiation received, or the total amount of radiation energy absorbed.

Dose rate

Rate at which exposure to radiation occurs and absorption takes place (dose rate= more damage w/ fast fate)

Cell sensitivity

more damage occurs in cells that are most sensitive to radiation, such as rapidly dividing cells and young cells

short-term effects

associated with large amounts of radiation absorbed in a short time

Acute radiation syndrome (ARS) is a type of __ effect

short term effect

symptoms of short-term effects

nausea, vomiting, diarrhea, hair loss, and hemorrhage.

Long-term effects

associated with small amounts of radiation absorbed repeatedly over a long period

Symptoms of long-term effects

linked to the induction of cancer, birth abnormalities, and genetic defects

Somatic effects

produce poor health in the irradiated individual; NOT transmitted to future generations

Genetic effects

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

radiosensitive

A cell that is sensitive to radiation

radioresistant

cell that is resistant to radiation

Radiosensitive organs

lymphoid tissues, bone marrow, reproductive cells, intestinal mucosa, skin, lens of eyes, and oral mucosa

Examples of radioresistant tissues

muscle tissue, nerve tissue, mature bone and cartilage, salivary gland, thyroid gland, kidney, and liver

critical organs include

thyroid gland, Bone marrow, Skin, Lens of the eye

three quantities of radiation

(1) exposure, (2) dose, and (3) dose equivalent.

two systems are used to define radiation measurements

(1) older system is referred to as the traditional system, or standard

system

(2) newer system is the SI system, or Système International d’Unités (International System of Units

traditional units of radiation measurement include…

Roentgen (R)

Radiation absorbed dose (rad)

Roentgen equivalent (in) man (rem)

The SI units of radiation measurement include the following

Coulombs/kilogram (C/kg), Gray (Gy), and Sievert (Sv)

exposure

measurement of ionization in air produced by x-rays.

roentgen (R)

The traditional unit of exposure for x-rays

How is roentgen measuring radiation exposure?

determining the amount of ionization that occurs in air.

Does any SI unit for exposure equivalent to roentgen exists?

No, exposure is stated in C/kg (coulombs per kilograms)

coulomb (C)

unit of electrical charge, number of ions pairs in kg of air

Dose

the amount of energy absorbed by a tissue

radiation absorbed dose, or rad

the amount of energy absorbed by a tissue, absorbed dose; doesnt take account the radiosensitivity of different tissue

The SI unit equivalent to the rad is__

gray (Gy)

1 rad =

0.01 Gy

1 Gy =

100 Rad

dose equivalent

measurement is used to compare the biologic effects of different types of radiation.

traditional unit of the dose equivalent is

roentgen equivalent (in) man, or rem.

SI unit equivalent of the rem is

sievert (Sv)

1 gy

100 REM

1 Sv =

100 rem

milli =

1/1000

micro =

1/1,000,000

Small unit to a big unit

divide

Big unit to small unit

multiply

background radiation

cosmic rays from outer space and the sun; radioactive potassium in food and

water; and radioactive material found within the human body.

free radical

uncharged (neutral) atom or molecule that exists with a single, unpaired electron

in its outermost shell.

effective dose

used to assess the potential for long-term effects that might occur in the future

formula for equivalent dose

Sv unit of Gy x QF

1 Sv =

1 Gy for dental x-rays

interactions of X-radiation

no interactions, absorption of energy and photoelectric effect, compton scatter and coherent scatter

no interaction

x-ray photon passes through the atom unchanged and leaves atom unchanged