Hall 5 - Fractionated RT & Dose-Rate Effect Flashcards
At high LET, is there potentially lethal damage?
No
What dictates whether there is potentially lethal damage?
Post-radiation conditions
If suboptimal for growth, more time to repair
What are the four R’s of radiobiology in order?
- Repair
- Reassortment
- Repopulation
- Reoxygenation
On average, when does sublethal damage occur?
2 hours after radiation
What did the split-dose experiment show?
Sublethal damage repair accounts for the increase in cell survival observed between fractions of RT
What is the mechanism of sublethal damage?
Repair of DSBs before they can interact to form lethal aberrations
As cells approach G2/M, they can counteract the effect of sublethal damage repair. How?
Increased radiosentivity
What part of the survival curve is represented by sublethal damage repair?
Shoulder
> > increase in survival when dose is fractionated over time
More SLD repair = more prominent shoulder = smaller alpha/beta
How does extent of SLD repair relate to alpha/beta?
More SLD = smaller alpha/beta
(more prominent shoulder on the survival curve)
With a single acute exposure, survival curve displays a ______ shoulder.
Prominent
With fractionation, survival curve displays a ______ shoulder.
Repeated (with each fraction)
Cells with more prominent survival curve shoulder demonstrate a ____ dose-rate effect.
Larger
Lower dose rate = ______ SLD repair
Less
0.1-1 Gy/min
> 1 Gy/min = alpha (no repair)
As dose rate decreases, shoulder _____ and survival becomes ______ function of dose.
Becomes shallower
Exponential
What happens to beta component when multiple small fractions of RT are used?
Goes to 0
Approximates a continuous exposure to a LDR source
Just alpha remains»_space; SF = e^(-aD)
Pure exponential; linear on log-linear plot
