Flashcards in Lecture 5 Deck (27):
Duration of Physical phase?
Duration of Chemical phase?
10^-10s to 1s
Duration of Biological phase?
late effects hrs to yrs
early effects sec to hrs
As LET increases RBE does what?
increases until a maximum where there is a subsequent drop off
Lethal effects of radiation are determined by what?
Cell survival not death
Survival curves express what?
Surviving fraction vs dose
As dose increases what happens to the surviving fraction?
at higher doses curve bends
lower doses curve straightens
What does the initial shoulder on a single dose curve represent?
Accumulation of sublethal damage
What occurs during recovery time of fractionated doses?
Repopulation and recovery not necessarily constant
What is the effect of high LET opposed to Low LET
more cells killed in a shorter time period
Can low LET be a good treatment for hypoxic cells?
No more radiosensitive in oxygen
What does a higher OER ratio indicate
Harder to kill
Cell damage caused?
Nucleus and DNA
Damage to Mitochondria
Damage to Lysosomes ( release enzymes digest internal structures)
Are children more sensitive to ionising radiation then others?
Yes as their cells have a higher metabolic rate
What is a dose modifier?
Increased free radicals no elemental oxygen in this
What is acute hypoxia?
Temporary closing or blockage of vessels
cells are too far away from capillary for oxygen to diffuse to them
Why does the tumour shrink during treatment?
Because a higher number of oxygenated cells are killed, as time progresses hypoxic cells become more oxygenated
When the number of hits is equal to the number of cells what happens?
63% of cells die and 37% survive
Indicates a highly radiosensitive cell when using the single target, single hit model
Indicates a highly radioresistant cell when using the single target, single hit model
Number of cells that would be killed with a D37 dose if there were no wasted hits?
What is the measure of the radiosensitivity of a cell when using the multitarget, single hit model
Indicates a highly radioresistant cell when using the multitarget, single hit model
indicates a highly radiosensitive cell when using the multitarget, single hit model
Mean Lethal Dose
Represented by D0 and is a constant related to the radiosensitivity of a cell
The dose required to reduce the survival fraction to 37% , is the slope of the straight line portion of the graph