LET & RBE Flashcards
what is a dose
amount of energy a patient receives
what is the prescribed dose
amount of radiation in terms of the absorbed dose
what is a gray
physical quantity of radiation
does short distances have a low or high LET
HIGH LET
what is the RBE
Relative biological effectiveness used for comparing different radiations by introducing a given biological effect
how can RBE be calculated
the ratio of dose which produces the same biological effect
what is the optimum LET
100 KeV/um
what types of LET do neutrons and alpha particles have?
neutron = high
alpha = even higher LET (doesn’t penetrate far)
what is LD50
Lethal Dose which kills 50% of all cells
What was the ratio for killing plants with neutrons and x-rays
LD50 X-rays = 6Gy
LD50 neutrons = 4Gy
1.5 : 1 therefore neutrons are 50% more effective
what is classed as wasted energy
any high LET energy which is undeposited at the DNA
what is LET
energy deposited per unit track
what is more effective at cell kill 1 Gy of high or low LET
high
what manner does high LET deposit at
a small and controlled manner
what doses are found with low LET x-rays
high doses
as LET increases, the curve becomes more steep
what sort of damage is low LET
indirect
what damage is high LET
direct
link high LET with RBE
it increases the RBE to a max, which then drops due to over kills
what factors affect RBE
- biological system or endpoint
- type of radiation and energy
- magnetic or particulate
- charged or uncharged
- dose level and number of fractions
- dose rate (low doses are more significant )
what proportions are DSB found at
low proportions
describe the RBE and neutrons relationship
- neutrons vary with dose per fraction
- fractionated regime for neutrons is greater than a single exposure, due to smaller doses
- RBE is larger for smaller doses
- neutrons are more efficient at doses per fraction
- this is reduced when the number of fractions increases
- RBE is larger at low dose rates than an acute exposure because of the n effectiveness decreasing with dose rate to a smaller extent than gamma and x-rays