radiation transfer Flashcards
most critical and radiosensitive target molecule.
Macromolecule.
DNA
liquid that contains dissolved substances, mixture of fluids such as water and alcohol is also a _____
solution
- breakage of the backbone of the long-chain macromolecule.
- result is the reduction of a long, single molecule into many smaller molecules, each of which may still be macromolecular.
- reduces not only the size of the macromolecule but also the viscosity of the solution.
MAIN-CHAIN SCISSION
Some macromolecules have small, spur-like side structures that extend off the main chain. Other spurs as a consequence of irradiation.
CROSS-LINKING
These side structures can behave as though they had a sticky substance on the end, and they attach to a neighboring macromolecule or to another segment of the same molecule.
cross-linking
- Radiation interaction with macromolecules also can result in disruption of single chemical bonds, producing ___
- are not detectable, but they can cause a minor medication of the molecule, which can cause it to malfunction within the cell.
POINT LESIONS
- The most abundant component of
protoplasm. - Protoplasm contains 80–85%water.
- Makes approximately 80–85% of a
person’s total body weight, and for several reasons is essential to life
water
- They are highly reactive.
● They are unstable and therefore exist
with a lifetime of 1 ms, however, during this time, they are capable of diffusion through cells or interaction at distant sites.
● They contain excess energy that can be transferred to other molecules to disrupt bonds and produce point lesions at some distance from the initial ionizing event
free radicals
principal damaging product after the radiolysis of water.
Hydroperoxyl radical
hydrogen peroxide
If the initial ionizing event occurs on the target molecule, the effect of radiation is
DIRECT
if the initial ionizing event occurs on a distant, non-critical molecule, which then transfers the energy of the ionization to the target molecule,
indirect effect
for a cell to die after radiation exposure, its target molecule must be inactivated
cell target theory
measure of the rate at which energy is transferred from ionizing radiation to soft tissue.
LET
LET of diagnostic x-ray is approximately
3 keV/μm.
in the absence of oxygen, the probability of a hit in the target molecule is low because of the relatively large distances between ionizing events
low LET radiation
the distance between ionizations is so close that the probability of a hit by a direct effect is high
high LET radiation
lAs the LET of radiation increases, the ability to produce biological damage also increases. This relative effect is quantitatively described by the _____
+ A measure of the efficiency of a particular radiation for producing a given biological endpoint.
relative
biological effectiveness (RBE).
without oxygen
anoxic
low oxygen
hypoxic
Tissue is more sensitive when irradiated in the oxygenated, or aerobic state than
when irradiated under anoxic (without oxygen) or hypoxic (low oxygen) conditions. This characteristic of the tissue is called the _____ and is described numerically by the ________
oxygen effect, oxygen enhancement ratio (OER).
is due to a repair mechanism inherent in the biochemistry of the cell. Some types of cells have greater capacity than others for repairs of sublethal damage.
intracellular recovery
Agents that enhance the effect of
radiation are called
radiosensitizers, sensitizing agents
examples of sentisizing agents
halogenated pyrimidines, methotrexate, actinomycin D,
hydroxyurea, and vitamin K.
These are compounds with molecules that contain a sulfhydryl group (sulfur
and hydrogen bound together) such as
cysteine and cysteamine.
Radioprotectors
