Lecture 5 Flashcards Preview

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Flashcards in Lecture 5 Deck (27):
1

Duration of Physical phase?

10^-15s

2

Duration of Chemical phase?

10^-10s to 1s

3

Duration of Biological phase?

late effects hrs to yrs
early effects sec to hrs

4

As LET increases RBE does what?

increases until a maximum where there is a subsequent drop off

5

Lethal effects of radiation are determined by what?

Cell survival not death

6

Survival curves express what?

Surviving fraction vs dose

7

As dose increases what happens to the surviving fraction?

Decreases
at higher doses curve bends
lower doses curve straightens

8

What does the initial shoulder on a single dose curve represent?

Accumulation of sublethal damage

9

What occurs during recovery time of fractionated doses?

Repopulation and recovery not necessarily constant

10

What is the effect of high LET opposed to Low LET

more cells killed in a shorter time period

11

Can low LET be a good treatment for hypoxic cells?

No more radiosensitive in oxygen

12

What does a higher OER ratio indicate

Harder to kill

13

Cell damage caused?

Nucleus and DNA
Cell membrane
Damage to Mitochondria
Damage to Lysosomes ( release enzymes digest internal structures)

14

Are children more sensitive to ionising radiation then others?

Yes as their cells have a higher metabolic rate

15

What is a dose modifier?

Increased free radicals no elemental oxygen in this

16

What is acute hypoxia?

Temporary closing or blockage of vessels

17

Chronic hypoxia?

cells are too far away from capillary for oxygen to diffuse to them

18

Why does the tumour shrink during treatment?

Because a higher number of oxygenated cells are killed, as time progresses hypoxic cells become more oxygenated

19

When the number of hits is equal to the number of cells what happens?

63% of cells die and 37% survive

20

Low D37

Indicates a highly radiosensitive cell when using the single target, single hit model

21

High D37

Indicates a highly radioresistant cell when using the single target, single hit model

22

Number of cells that would be killed with a D37 dose if there were no wasted hits?

100

23

What is the measure of the radiosensitivity of a cell when using the multitarget, single hit model

D0

24

High D0?

Indicates a highly radioresistant cell when using the multitarget, single hit model

25

Low D0?

indicates a highly radiosensitive cell when using the multitarget, single hit model

26

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

27

DQ (Threshold dose)?

a measure of the width of the shoulder of the curve related to the capacity of the cell to recover from the sublethal damage