Radl 70 Principles of Radiobiology

atomic level

cellular level

ionization

• 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

• 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

• 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

• pertains to how much oxygen in the tissue
• the more oxygen there is the more damage can occur
• more important in rad therapy

radiation

the tissue being irradiated

• master molecules
• dna
• rna
• enzymes
• proteins

• compton
• photoelectric

• results in breakage of the master molecule's chemical bonds
• will result in a malfunction of that particular molecule
• sets off biologic domino effect

interaction of x-ray photons w/ non master molecules mostly water

radiolysis of water- xray hitting a water molecule

• a positive water molecule HOH+
• an electron

3

• the positively charge water molecule recombines with an electron
• a stable water molecule is formed
• no damage is done

• 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

• 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

the damage caused by the byproduct of radiation (ions) with the macromolecule, not the radiation itself

hydrolysis of water

• 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

gene mutations

low LET

high LET

• one or more breaks in each of the two sugar-phosphate chains
• not repaired as easily as a single strand break

two interactions hit on each side of the sugar phosphate chain

• 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

• can join to another fractured chromosome
• new formations are known as an aberration

• when a broken chromosome rejoins with the broken piece
• no damage

when a part of a chromosome is lost in the next division

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

cell death will occur if the master molecule in that cell is inactivated by radiation exposure

target theory

• will be seen in future generations
• this is why we shield gonads

individual consequences only

• nonspecific
• cant tell if an effect came from radiation or someting else

no

• 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

• 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

• no
• it can no longer pass damage to future generations

• interphase is cut short
• doesnt mean the cell dies completely

• occurs when the cell dies after one or more divisions
• can occur from very small doses

• the cell fails to divide on time
• as little as 1 rad

• yes
• permanent or temporary
• cell can recover and continue to funtion if repair enzymes are able to fix the damage

• skin
• intestinal crypt cells
• reproductive cells

• brain
• muscle
• nerve cells

• LET
• presence of oxygen
• cancer cells are often hypoxic- hyperbaric oxygenation of pts before treatment. makes them more sensitive to radiation

• cells are the most sensitive if theyre:
• youngest
• least specialization or differentiation
• graetest reproductive activity
• longest mitotic phases

hematologic depression within a few days

lymphocytes or white blood cells

25

• radiosensitive
• it is constantly regenerated by the body

radioinsensitive

• radioinsensitive
• highly specialized and do not divide
• developing nerve cells are highly radiosensitive in the fetus

5000 rads

radiosensitive

can cause temporary sterility for about a year in the male

500-600 rads

10 rads

no

• 200 rads temp
• 500 rads perm

10 rads

0-25 rads

0-200 rads

• estimates the risk of associated with low-level radiation
• leukemia, breast cancer, heritable damage

nonstochastic effects such as skin erythema and hematologic depression

• 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

• quantity of radiation recieved
• ability of ionizing radiation
• amount of body area exposed
• specific body parts exposed

• 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