Lesson 7: Principles of Radiobiology Flashcards
What is radiation biology
- effects of ionizing radiation on living systems
- includes events occuring after the absorption of energy from ionizing radiation
- injury from the living system that may be produced
Adverse effects caused by radiation
- happens at a cellular level (we dont really notice)
Tissue and radiation interactions
- damage may/may not result
- a matter of chance
-90% of interactions are harmless
Visible damage from radiation
- indistinguishable from other causes (smoking chemicals etc)
- difficult to determine if low levels of radiation cause damage
How does ionizing radiation damage living systems
- compromising the molecular structure
- gamma and xrays are ionzing and penetrating
- alpha particles dont penetrate (cause more damage if inhaled)
3 radiation energy transfer determinants
- charge mass and energy of radiation
Linear Energy transfer
- the average amount of energy deposited as ionzing energy passes through a medium (per unit length of track)
- increased LET increases the chance of producing a significant biological response
- closer the damage is together the harder for the body to repair ie alpha particles form a lot of ionizatioins in a small area
High LET
- alpha particles
- less penetrating
- dense ionzations
- many ionizations/short distance travelled
Why the concern of LET
more likely for DNA to be struck and damaged in a high LET interaction
Relative Biologic Effects
- the relative capabilities of radiation with differing LETs to produce a biologic reaction
- a measure of the damage that will occur in comparison with the same radiation dose
Radiation Weighting Factor
used to calculate equivalent dose
- determines the ability of any kind of ionizing radiation to cause biological damage
- X-ray 1
- Alpha 20
Oxygen Enhancement Ratio
ratio of radiatin dise to cause damage in oxygen deprived environment to the dose required to cause an identical response in normal oxygenated conditions
What is cell radiosensitivity
Equal doses of ionizing radiation produce different degrees of damage in
different kinds of human cells because of differences in cell radiosensitivity.
* The more mature and specialized in performing functions a cell is, the less
sensitive it is to radiation
Law of Bergonie and Tribondeau
- radiosensitivity of cells is directly proportional to the reproductive activity and inversely proportional to their degree of differentiation
- most radiosensitive cells are:
immature
unspecialized
high reproductive activity
bone marrow
blood cells
GI and urinary system
Red blood cell sensitivity
- most sensitive in bone marrow because theyre immature and still in development
Radiosensitive vs radioresistant cells
- basal cells of the skin
- blood cells
radioinsensitive
- brain cells
- muscle cells
- nerve cells
Target Theory
a key molecule that maintains normal cell function is believed to be present in every cell
- DNA is the target
- necessary for survival of the cell
Classification of ionizing interactions
Direct action- DNA
indirect action - H2O
Radiolysis of Water
- dissociation of water due to ionization
- produces free radicals
- production of undesirable chemical reactions and damage
- increases effective target size
Step 1 of radiolysis
Ion Pair
Water hit with xray and e- is ejected
- HOH+ and e-
- HOH+ is unstable
sometimes e- just reconnects to water and no damage occurs
Step 2 of radiolysis
- HOH+ is unstable breaks apart and makes H+ ion and OH radical
OR
free electron connects to other water molecule makes HOH-
makes hydrogen radical and OH-
Radicals
H* and OH* have excess energy and can transfer this energy to the other molecules
2 OH* make hydrogen peroxide which causes cell death
H* and O2 make hydroperoxyl radical
