Lecture 5

Question 1

Duration of Physical phase?

Answer 1

10^-15s

Question 2

Duration of Chemical phase?

Answer 2

10^-10s to 1s

Question 3

Duration of Biological phase?

Answer 3

late effects hrs to yrs

early effects sec to hrs

Question 4

As LET increases RBE does what?

Answer 4

increases until a maximum where there is a subsequent drop off

Question 5

Lethal effects of radiation are determined by what?

Answer 5

Cell survival not death

Question 6

Survival curves express what?

Answer 6

Surviving fraction vs dose

Question 7

As dose increases what happens to the surviving fraction?

Answer 7

Decreases
at higher doses curve bends
lower doses curve straightens

Question 8

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

Answer 8

Accumulation of sublethal damage

Question 9

What occurs during recovery time of fractionated doses?

Answer 9

Repopulation and recovery not necessarily constant

Question 10

What is the effect of high LET opposed to Low LET

Answer 10

more cells killed in a shorter time period

Question 11

Can low LET be a good treatment for hypoxic cells?

Answer 11

No more radiosensitive in oxygen

Question 12

What does a higher OER ratio indicate

Answer 12

Harder to kill

Question 13

Cell damage caused?

Answer 13

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

Question 14

Are children more sensitive to ionising radiation then others?

Answer 14

Yes as their cells have a higher metabolic rate

Question 15

What is a dose modifier?

Answer 15

Increased free radicals no elemental oxygen in this

Question 16

What is acute hypoxia?

Answer 16

Temporary closing or blockage of vessels

Question 17

Chronic hypoxia?

Answer 17

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

Question 18

Why does the tumour shrink during treatment?

Answer 18

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

Question 19

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

Answer 19

63% of cells die and 37% survive

Question 20

Low D37

Answer 20

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

Question 21

High D37

Answer 21

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

Question 22

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

Answer 22

100

Question 23

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

Answer 23

D0

Question 24

High D0?

Answer 24

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

Question 25

Low D0?

Answer 25

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

Question 26

Mean Lethal Dose

Answer 26

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

Question 27

DQ (Threshold dose)?

Answer 27

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