Cell survival curves Flashcards
what is a cell survival curve
- a curve that describes the relationships between radiation dose and the proportion of cells that survive
What are the two survival models
single-target - single hit
Multi-target - single hit
What is the single-target - single hit model
according to the law of probability when the number of projections equals the number of targets, only 63% of targets will be hit, 37% will survive.
This is because sometimes the projections hit the same target, this is useless as after the first hit the target is dead.
What is D37
This represents the percentage of survival.
What does it mean if D37 is low
that it represents a highly radiosensitive organ
What does it mean if D37 is high
That it represents a radioresistant organ, ( it takes a high dose to kill 63% of cells)
What is the Multi-target - single hit model
This applies to more complex beings like humans, where it takes multiple hits to kill a cell (there are two targets), because both targets must be hit for cell death survival at low doses is almost 100%.
When the cell is hit once it may be able to repair any damage, therefore a threshold dose exists, this is called the quasi threshold dose DQ
What is DQ
It relates to the capacity a cell has to recover from sublethal damage, cells may die if DQ is exceeded
What does a large DQ indicate
That a cell is more likely to recover from sublethal doses of radiation.
As dose increases, more cells are hit for the first time, and as it keeps increasing..
more cells are killed for the second time
An outcome of low LET radiation can result in damage being repaired by
sub lethal damage, and lethal damage
How does sublethal damage repair occur
when two radiation doses are separated by time sublethal damage repair occurs, the damage that is accumulated before the cell dies is sublethal damage.
Can sublethal damage usually be repaired
yes, unless another radiation dose is given
what is an example of cells that show little repair of sublethal damage
Bone marrow cells
How does potentially lethal damage occur
Damage that can be repaired between radiation and subsequent radiation, it occurs when conditions are modified post-irradiation. Damage has the potential to develop but will only do so if the conditions post-irradiation are optimal for cells to divide to sustain more damage.
