*RPB L5- Cell Survival Curves Flashcards
What does “clonogenic” mean?
Think of it as “Clone”- means that a cell is able to replicate itself… proliferate indefinitely
What does “reproductive death” mean?
For cells that can no longer grow - they are technically still ‘alive’, however they are DEAD as they cannot replicate anymore
What does “proliferate” mean?
Able to divide (in this case, replicate) indefinitely
What factors affect the shape of the curve?
OER, LET, cell cycle, cell type, total dose, dose rate…
What is the x and y axis on the cell survival curve?
x: dose rate, y is cell survival in LOG (so we can get a linear line)
Why is the cell survival semi-log??
Semi-log scale because we want our line to be linear - easier for calculations
How much dose do you need to destroy
1. non-proliferating cells
2. proliferating cells
Explain why
- 100Gy
- 2Gy
Because dividing/growing cells are more radiosensitive than non-growing cells
You saw how when there is DNA damage, you can have the sticky ends joining, or you can have diccentric rings; can these still replicate?
NO!
What is the difference between in vitro and in vivo?
Vivo is inside organism, vitro is like in petri dish
What is the relationship between dose and survival? (i.e. linear, cubic, quad, log…)
LINEAR: Increase dose, decrease cell survival
What is “plating efficiency”?
Exactly what it sounds like - how efficient the ‘plate’ is - glass plate maybe?
What is surviving fraction?
How many cells survived after radiation (on the petri disk); there is a formula for this
What are the three types of results of radiation damage?
- Sublethal
- Lethal
- Potentially lethal
What is lethal DNA damage?
Cannot be reversed. It’s gone!
Where does radiation usually target?
DNA
What is mitotic death?
Death of the cell when it tries to divide - has lost its proliferative ability
What is sub-lethal damage?
Damage that can be repaired, if given time
What is potentially lethal damage?
Depends on environment - depends on the post-environmental conditions i.e. Giving oxygen
What is the shape of the survival curve for densely ionising radiation and sparsely ionising radiation?
Dense would be very steep, no shoulder, straight down. Sparse would have a shoulder, mix of quadratic and linear line
What is Dq?
QUASITHRESHOLD - the ‘threshold’ where no damaging is taking place up until this dose threshold
Cell survival curve: It is both linear and quadratic. What do they represent?
Linear part is when there is 1 irradiation event that breaks both DNA strand. Quadratic is related to breaks due to 2 separate events - Think of it as like Linear = alpha, str8 kill
Is high or low LET curve a straight line? Why?
High - More Linear Energy Transfer means more damage done = i.e. alpha particle is linear line
Does sparse or dense ionising radiation have a linear curve?
DENSE
If you were given x-rays, neutrons and alpha particles, which one would be steepest to least steep in survival curve?
alpha steepest, neutrons middle, x-rays least steep
In the survival curve formula, can you actually tell which DNa is getting hit by alpha/which getting hit by beta?
No, this formula is kinda just a mathematical formula for us to use
Define Quasithreshold
Dq is the dose at which the linear portion of the survival curve, extrapolated backward, cuts the dose axis drawn through a survival fraction of unity (100%)
What is extrapolation number?
this is ‘n’; tells us about the shoulder of the curve. It is the width of the shoulder. If n is large, shoulder is broad
How do you find D0 on graph?
CHOOSE A LINEAR PART!! Doesn’t matter where, just choose a part and go to approx 37%
What does it mean if you see the cell survival curve with lots of repeated shoulders?
FRACTIONATION of dose
What is the “bystander effect”?
It is when cells closeby to those cells that are directly irradiated by a charged particle gets damaged
When is the bystander effect most pronounced?
When the cells are joined by gap-junctions: 30% bystander cells will die
What is apoptosis and mitotic death?
You know this already!
What is AUTOPHAGY? How is it different from apoptosis?
AUTOPHAGY - self eating: using lysosomes. apoptosis is programmed cell death.
Autophagy is a type (2) of apoptosis
What is senescence? What protein is involved?
A type of cell death - when the cell is stressed out… p53 and Rb (Rubbish bin… lol) and 53kg…
If a response to radiation is expected, no matter how small the dose, then that dose-response is _____.
Threshold or non-threshold?
non-threshold; like alpha particles?
Radiation induced genetic damage follows a _____ dose-response relationship.
Linear-non-threshold or linear-threshold
Linear non-threshold
In a linear qudratic model, is alpha or beta constant smaller?
Beta- because alpha is more steep
The mean probability of one particle causing a lesion is linearly proportional to dose
True
