Radl 70 Principles of Radiobiology
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most effects of radiation begin where?
most effects of radiation manifests where?
chemical and biological effects are determined by the degree of what within the tissue?
describe low let radiations
- from x or gamma rays
- short wavelength, high energy waves
- sparsely ionizing
- randomly interact
- do not give up energy quickly
- damage is usually indirectly- free radicals are formed
- may cause single-strand breaks in one side of the DNA ladder
- usually sublethal- repair enzymes reverse the damage
describe high LET radiation
- from particles that possess mass and charge
- alpha particles, particles released from interactions between neutrons and atoms
- lose energy rapidly than x or gamma
- produce more ionization per unit length of travel
- energy is spent sooner than x or gamma
high or low LET radiation is more likely to interact with DNA
what is relative biological effectiveness?
- the ability of radiation with different LET to produce a biologic reaction
- x-ray is usually compared to a different source that will produce the same effect
- expressed as a ratio
- LET and RBE pertains to radiation
what is oxygen enhancement ratio?
- pertains to how much oxygen in the tissue
- the more oxygen there is the more damage can occur
- more important in rad therapy
what does LET and RBE pertain to?
what does OER pertain to?
the tissue being irradiated
what type of molecules does direct action pertain to?
- master molecules
what type of radiation interactions can occur during a direct action?
how is direct action harmful?
- results in breakage of the master molecule's chemical bonds
- will result in a malfunction of that particular molecule
- sets off biologic domino effect
what is indirect action?
interaction of x-ray photons w/ non master molecules mostly water
what is an example of indirect action?
radiolysis of water- xray hitting a water molecule
radiolysis of water produces what types of ions?
- a positive water molecule HOH+
- an electron
how many different reactions can occur after radioloysis of water (HOH+, e-)?
Reaction 1 that can occur after radiolysis of water
- the positively charge water molecule recombines with an electron
- a stable water molecule is formed
- no damage is done
Reaction 2 that can occur after radiolysis of water
- the electron joins with a water molecule
- a negative water ion is formed
- the positive and negative water molecules are unstable
- these can break apart into smaller molecules
- free radicals can be formed by this breakup
- these objects are highly reactive and can do cellular damage
Reaction 3 that can occur after radiolysis of water
- two of the free radicals can recombine to form hydrogen peroxide
- highly toxic to cell
- about two-thirds of all biologic damage is caused by the reaction 2 and 3
what is indirect action?
the damage caused by the byproduct of radiation (ions) with the macromolecule, not the radiation itself
what is one of the main precursors of indirect action?
hydrolysis of water
what is point mutation
- ionizing radiation that rupturesthe chemical bond of a macromolecule severing one of the sugar-phosphate chain siderails of the DNA ladder
- single strand break
- repair enzymes can reverse this damage
what may result with point mutation?
what type of LET radiation can cause point mutation (single strand break)?
What type of LET radiation can cause a double strand break?
what happens in a double strand break?
- one or more breaks in each of the two sugar-phosphate chains
- not repaired as easily as a single strand break
what causes cleaved chromosomes?
two interactions hit on each side of the sugar phosphate chain
what is a cleaved chromosome?
- chromosome that is broken in two
- each new portion contains an unequal amount of genetic material
- can then divide into defective daughter cells
- know as mutation
what happens if a chromosome is broke to two or more fragments?
- can join to another fractured chromosome
- new formations are known as an aberration
what is restitution?
- when a broken chromosome rejoins with the broken piece
- no damage
what is deletion?
when a part of a chromosome is lost in the next division
what is a broken end rearrangement?
when a chromosome recombines with another piece of chromosome that appears like a restitution but the genetic material has been rearranged that will alter its function
what is target theory?
cell death will occur if the master molecule in that cell is inactivated by radiation exposure
which theory is used to explain cell death and nonfatal cell abnormalities caused by radiation exposure?
what happens if mutation is genetic?
- will be seen in future generations
- this is why we shield gonads
what if mutation is somatic?
individual consequences only
are radiation effects specific or nonspecific?
- cant tell if an effect came from radiation or someting else
are there certain cancers that are unique to radiation?
how much radiation does it take to cause instant death?
- 1000 gray of x or gamma ray in a period of seconds or a few minutes
- 100,000 rads
- radiation this high do not occur in the diagnostic or therapeutic ranges
how much radiation does it take for reproductive death to occur?
- 1-10 gray
- 100-1000 rads
- cell does not die, but becomes sterile
- cell will continue to metabolize and synthesize nucleic acids and proteins
- transmission of damage to future generations is prevented
when a germ cell becomes sterile from radiation exposure, can it transmit its damages to future generations?
- it can no longer pass damage to future generations
what is interphase death?
- interphase is cut short
- doesnt mean the cell dies completely
what is mitotic death?
- occurs when the cell dies after one or more divisions
- can occur from very small doses
what is mitotic delay? how much radiation?
- the cell fails to divide on time
- as little as 1 rad
can radiation interfere with a cell's function? if so, is it permanent or temporary? can it be fixed?
- permanent or temporary
- cell can recover and continue to funtion if repair enzymes are able to fix the damage
which cells are very sensitive to radiation?
- intestinal crypt cells
- reproductive cells
which cells are radioinsensitive?
what other factors contribute to cell radionsentivity besides the cell's structure?
- presence of oxygen
- cancer cells are often hypoxic- hyperbaric oxygenation of pts before treatment. makes them more sensitive to radiation
what does law of bergonie and tribondeau state?
- cells are the most sensitive if theyre:
- least specialization or differentiation
- graetest reproductive activity
- longest mitotic phases
what happens to the blood cells when the whole body is exposed to 25 rad?
hematologic depression within a few days
which cells are the most susceptible to radiation?
lymphocytes or white blood cells
how many rads will it take to depress the number of lymphocytes in circulating blood?
is the epithelial tissue radiosensitive or radioinsensitive? why or why not?
- it is constantly regenerated by the body
are muscle tissue radiosensitive or radioinsensitive?
are nerve tissue radiosensitive or radioinsensitive?
- highly specialized and do not divide
- developing nerve cells are highly radiosensitive in the fetus
how much radiation does it take to destroy the nervous system?
are reproductive cells radiosensitive or radioinsensitive?
what can 200 rads do to reproductive cells?
can cause temporary sterility for about a year in the male
how much radiation can cause permanent sterility?
how much radiation does it take to depress the sperm count?
in the female, does the ova divide constantly?
how much radiation to the ovaries does it take to cause temporary sterility? permanent sterility
- 200 rads temp
- 500 rads perm
how much radiation does it take to cause menstrual irregularities
what would be the treshhold range to depress white blood cells?
what would be the threshold range for temporary sterility?
what does the linear nonthreshold curve estimate? what are some examples?
- estimates the risk of associated with low-level radiation
- leukemia, breast cancer, heritable damage
what is the linear-threshold curve used for?
nonstochastic effects such as skin erythema and hematologic depression
what does the non-linear threshold curve determine?
- used to determine high dose response in radiation therapy
- indicates the existence of a threshold
- for ex:
- cataracts and blindness: once pt is blind, even higher radiation can no longer do damage to the eyes because it recieved the max damage
what factors determine somatic and genetic damage?
- quantity of radiation recieved
- ability of ionizing radiation
- amount of body area exposed
- specific body parts exposed
What can cause the greatest amount of biologic damage?
- large dose of high LET delivered to a large or radiosensitivity area of the body
- for ex: 1000 rads of alpha particle to the gonads is more damaging than 1000 rads of alpha to the head
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