chapter 3: radiation biology

what can radiographs reveal?

asymptomatic conditions

what can radiographs confirm/contradict?

clinical observations

what are risks of radiation?

1. unwanted changes in living cells

2. damage for generations 

what are the 2 types of radiation injury?

direct and indirect effect

what is a direct effect radiation injury?

direct “hit”/ionization and damage of critical structures by x-ray photons

how often do direct effect radiation injuries occur?

rarely

what is an indirect effect radiation injury?

cell damage due to formation of toxins 

what does ionization of water lead to?

free radicals

what do free radicals combine to form?

toxins

how often do indirect effect radiation injuries occur?

commonly, water abundant

what happens in coherent scatter?

photon passes by an atom without changing atomic structure, but its electrons’ energy make photon change its path

what also happens during compton scatter?

ionization

what percent of x-ray beam scatter does compton scatter make up?

60% 

what percent of scatter does the photoelectric effect make up?

30%

what also happens during the photoelectric effect?

ionization

what happens during the photoelectric effect?

a photon uses all of its energy to eject a photoelectron

what happens to an ejected photoelectron in photoelectric effect?

can interact with atoms and molecules in potentially dangerous ways

what can ionization do to a cell?

cause direct injury

what are free electrons? 

unstable 

what is a free radical?

a molecule with a single unpaired electron in the outermost shell

what are some traits of free radicals?

highly reactive and unstable

what are free radicals involved in?

degenerative diseases and cancers

what is the primary form of cell damage from radiation?

free radicals 

when are free radicals formed?

when an x-ray photon ionizes water

why do free radicals occur so often?

because our bodies are primarily made of water

what is water radiolysis?

when a water molecule gets ionized and decomposes into hydrogen and hydroxyl radicals

what is the product of water radiolysis? 

hydrogen and hydroxyl radicals 

free radicals can result in what?

1. combine with free radicals and become stable

2. turn into toxins

what is the dose response curve?

the graph of relationship between dose and damage risk

what are the 2 categories of negative effects of ionizing radiation?

stochastic and non-stochastic

what is stochastic AKA?

probabilistic or random 

what is stochastic effect?

change of an effect is a direct function of the dose without a threshold

what happens as dose increases for stochastic effects?

the probability of a biological effect increases too

what does the increasing dose not affect in stochastic effects?

severity of biological effect

why do stochastic effects occur?

due to ionization effects on chromosomes and genetic mutation 

what is non-stochastic AKA?

deterministic effect

when do non-stochastic effects occur?

when a threshold of doses is reached

what happens to severity as dose increases in non-stochastic effects?

severity also increases

what are non-stochastic effects due to?

major cell damage/death 

what could happen after damage from ionizing radiation?

1. cell may repair itself completely

2. cell may die if DNA is beyond repair (non-stochastic)

3. DNA may repair incorrectly (stochastic)

what could happen if DNA repairs incorrectly?

damage can transfer to daughter cell, can later lead to cancer

what is latent period?

time from exposure to observable effects 

what shortens latent period?

higher dose and faster rate

what is period of injury?

time of cell damage/death, chromosomal changes, mitotic changes

what is the recovery period?

repair is more likely with low level radiation

what factors impact radiation injury?

1. total dose 

2. dose rate 

3. amount of tissue 

4. tissue sensitivity 

5. age 

what kind of dose rate causes more damage?

high dose rate

why does a high dose rate cause more damage?

rapid delivery of radiation doesn’t give cells enough time to repair

what is localized exposure?

targeting specific areas of the body

what is generalized exposure?

all over exposure of the entire organism 

when do short term effects occur?

after large doses of radiation, minutes-weeks after exposure

what can happen during short term effects?

cells can be killed, enough damage to harm tissue/organs

what is an example of short term effects?

acute radiation syndrome

when does acute radiation syndrome occur?

after full body exposure to high dose of radiation in a short amount of time (usually minutes)

what causes long term effects?

chronic, repeated low doses

when do long term effects kick in?

not immediately

what are somatic effects?

affects non-reproductive cells

what are genetic effects?

doesn’t cause illness in organism but causes damage in next generation 

are cells with high mitotic activity more sensitive or resistant?

sensitive

what does high mitotic activity mean?

cells divide more frequently

are immature cells more sensitive or resistant?

sensitive

are cells that aren’t highly specialized more sensitive or resistant?

sensitive 

are cells with a high metabolism more sensitive or resistant?

sensitive

what are examples of sensitive cells?

blood cells, immature reproductive cells, young bone cells

what are examples of resistant cells?

bone cells, muscle cells, nerve cells

what are examples of radio-sensitive tissues?

lymph tissue, bone marrow, testes, intestines 

what are examples of resistant tissues?

salivary glands, kidneys, liver

what are examples of critical organs?

thyroid, bone marrow, skin, lens of eye

what is exposure measurement?

amount of radiation in the air that the patient is exposed to

what does the concentration of exposure measurement depend on?

volume of air 

what is dose measurement?

amount of energy absorbed by tissue

what is dose equivalent measurement?

dose relative to biological impact of radiation type

what is exposure rate?

dose of exposure/unit of time

what is a roentgen (R)? 

measure of radiation based on amount of ionization in the air 

what does 1R equal?

~2 billion ion pairs in 1 cubic cm of air

what is radiation absorbed dose (rad)?

unit of measuring the amount of radiation energy absorbed by matter

what is 1 rad equal to?

100 ergs of energy per gram of tissue (100 erg/g)

what is a roentgen equivalent man (rem)?

unit of measurement to compare biological effects of different kinds of radiation in the body 

what is a curie (Ci)?

traditional unit of radioactivity

what is 1 Ci equal to?

3.7 × 10^10 decays per second

what are coulombs per kilogram equal to?

roentgen

what is 1 C/kg equal to?

3876 R 

what is 1 gray (Gy) equal to?

100 rads

what is a sievert (Sv) equal to?

100 rems

what is a becquerel (Bq) equal to?

1 nucleus decay per second

1 Ci = how many Bq?

1 Ci = 3.7 × 10^10 Bq 

what units are used to measure exposure (radiation in air)?

roentgen (R) and coulomb/kg

what units are used to measure absorbed dose of radiation?

rad and gray (Gy)

1 Gy = how many rad?

1 Gy = 100 rad

100 rad = how many Gy?

100 rad = 1 Gy

what units are used to measure equivalent dose (weighted biological effect of absorbed dose)?

rem and sievert (Sv) 

1 Sv = how many rems?

1 Sv = 100 rem

100 rem = how many sieverts?

1 Sv

what units are used to measure radioactivity?

curie (Ci) and becquerel (Bq) 

1 Ci = how many Bq?

1 Ci = 3.7× 10^10 Bq

3.7×10^10 Bq = how many Ci?

3.7×10^10 Bq = 1 Ci

what is the radiation weighting factor (Wr)?

used to determine equivalent dose for uniform whole body exposure 

what is the Wr for photons?

1

what is the Wr for electrons?

1

what is the Wr for protons?

2