*** Basic Biologic Interactions Of Radiation Flashcards
Interaction of radiation in cells
Probability function
Initial deposition of energy occur very rapidly
Period of approximately 10^-17 seconds
Radiation interaction in a cell
Non-selective
Ratio of the doses under hypoxia to aerated conditions that produce the same biological effect
Oxygen enhancement ratio (OER)
Increases radiation effectiveness for cell killing
Oxygen presence (aerated conditions)
Result in more radio resistant cells
Lack of oxygen (hypoxic cells)
Cells are much more sensitive to x-rays in the presence of molecular oxygen than its absence
Oxygen effect
Rate at which energy is energy is deposited as a charged particle travels through matter
LET (Linear energy transfer)
Unit for LET
keV/u
Low LET radiation
Electromagnetic radiation
High LET radiation
Particulate radiation
Ability of different types of radiations to produce a specific biologic response
Relative biologic effectiveness (RBE)
Comparison of a dose of a test radiation to a dose of 250keV X-rays which produce the same biologic response
RBE
Involves absorption of ionizing radiation in the medium in which the molecules are suspended
Indirect action
Occurs when an ionizing radiation interacts with and is absorbed by a biologic macromolecules
Direct action
Absorption of radiation by a water molecule results in the production of ion pair and free radicals
Radiolysis of water
Contain a single unpaired electron in their outer shell, making them chemically unstable and highly reactive
Free radicals
Recombining with other free radicals producing ___, a toxic substance to the cell
Hydrogen peroxide
Requires a higher radiation dose to produce measurable effect than in vivo irradiation
In vitro irradiation of macromolecules
More sensitive in their natural state
Molecules
Three major effects of in vitro irradiation of macromolecules
Main-chain scission
Cross-linking
Point lesions
Breakage of thread or backbone of long chain of macromolecules resulting to reduction of long, single molecule into many smaller molecules
Main-chain scission
After breakage, the broken end will attach to a neighboring macromolecules
Cross-linking
Disruption of a single chemical bonds of a macromolecules
Point lesions
Molecules that are present only in necessary amount, and all are constantly needed for the proper functioning and life of cell
Target
Interaction of ionizing radiation with a “key molecule” within a short distance around one of these molecules
Target theory
Occurs only if target molecule is inactivated
Cell death
Most likely target for radiation action
DNA
Fracture in the back bone of one chain of the DNA molecule
Single strand break
Fracture in the backbone if both chains of DNA molecule
Double strand break
Principal characteristic of radiation-induced malignant disease
Uncontrolled rapid proliferation of cells
Molecules with excess energy that diffuse through the cell and disrupt molecular bonds of target molecule
Free radicals
Required rads to kill a cell when nucleus is irradiated
100rads
Required rads to kill a cell when cytoplasm is irradiated
1000 rads
Changing a normal cell into a malignant cell
Transformation
Types of chromosomal mutation
Single break effect
Double break effect
Chromosome stickiness
Rejoining and healing of the broken ends of the chromosome
Restitution
Joining of 2 chromatids without a centromere
Acentric chromosome
Joining of two chromatids with centromeres
Dicentric chromosome
Joining of Acentric fragment from one chromosome to the fragment containing the centromere of the other chromosome
Translocation
Associate with translocation of chromosomes
Leukemia
Process wherein the fragments between the break is deleted
Deletion
The fragment with broken ends turn around and rejoin thereby reversing its position on the chromosome
Inversion
Results when broken ends of the fragment with the centromere moves about and twist before joining
Ring chromosome
Occurs in cell already in division; believed by alteration in the chemical composition of the protein component of the chromosome by irradiation
Chromosome stickiness
Rate at which radiation is delivered
Dose rate
Produce more simple aberrations than complex ones
Low LET radiations
Greater possibility of producing more complex aberration
High LET radiation
Study of the sequence of events that follows the absorption of energy from ionizing radiation…
Radiobiology
