Lecture 5 Flashcards Preview

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Flashcards in Lecture 5 Deck (27)
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1
Q

Duration of Physical phase?

A

10^-15s

2
Q

Duration of Chemical phase?

A

10^-10s to 1s

3
Q

Duration of Biological phase?

A

late effects hrs to yrs

early effects sec to hrs

4
Q

As LET increases RBE does what?

A

increases until a maximum where there is a subsequent drop off

5
Q

Lethal effects of radiation are determined by what?

A

Cell survival not death

6
Q

Survival curves express what?

A

Surviving fraction vs dose

7
Q

As dose increases what happens to the surviving fraction?

A

Decreases
at higher doses curve bends
lower doses curve straightens

8
Q

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

A

Accumulation of sublethal damage

9
Q

What occurs during recovery time of fractionated doses?

A

Repopulation and recovery not necessarily constant

10
Q

What is the effect of high LET opposed to Low LET

A

more cells killed in a shorter time period

11
Q

Can low LET be a good treatment for hypoxic cells?

A

No more radiosensitive in oxygen

12
Q

What does a higher OER ratio indicate

A

Harder to kill

13
Q

Cell damage caused?

A

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

14
Q

Are children more sensitive to ionising radiation then others?

A

Yes as their cells have a higher metabolic rate

15
Q

What is a dose modifier?

A

Increased free radicals no elemental oxygen in this

16
Q

What is acute hypoxia?

A

Temporary closing or blockage of vessels

17
Q

Chronic hypoxia?

A

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

18
Q

Why does the tumour shrink during treatment?

A

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

19
Q

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

A

63% of cells die and 37% survive

20
Q

Low D37

A

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

21
Q

High D37

A

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

22
Q

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

A

100

23
Q

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

A

D0

24
Q

High D0?

A

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

25
Q

Low D0?

A

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

26
Q

Mean Lethal Dose

A

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
Q

DQ (Threshold dose)?

A

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