* RBP 7: Dose Rate & Effects

Question 1

What are the types of Radiation Damage?

Answer 1

LD, PLD, SLD

Question 2

What does Lethal dose mean?

Answer 2

Dose at which all cells are killed and CAN NOT be revived

Question 3

What does PLD mean?

Answer 3

Radiation damage that can be modified by postirradiation environmental conditions - i.e. Oxygen effect. Depends on ENVIRONMENT

Question 4

What is SLD?

Answer 4

Can be repaired in hours unless additional sublethal damage is added. Depends on TIME

Question 5

What is the main diff between PLD and SLD?

Answer 5

PLD depends on environment, SLD depends on time

Question 6

Describe the curve of the Dose Rate Effect (you did this last night!)

Answer 6

There are three parts to it: SLDR, Reassortment, Repopulation. The SF increases with SLDR (as cells repair), then decreases at reassortment as cells enter the sensitive stage PLUS the second dose is given. Then, repopulation, SF increases again.

Question 7

What is SLDR?

Answer 7

Sub lethal damage repair; it is when a dose is split into 2 parts, and the time between this doses is when cells have time to repair

Question 8

Why does reassortment decrease cell survival?

Answer 8

Because the cells that were in the resistive phase are now entering a sensitive phase; then the second part of the dose is given (fractionated) and this then kills those cells

Question 9

What are 3 ways in which you can alter the effect of radiation (general)

Answer 9

1. Dose rate
2. Environment - OER
3. Fractionation

Question 10

How do you calculate OER? What is that one thing you keep forgetting! Gurl don’t!

Answer 10

OER = D0 Hypoxic / D0 aerobic

DONT FORGET TO MEASURE FROM D0!!!

Question 11

What is OER?

Answer 11

The ratio of the dose of hypoxic to aerobic needed to have the same biological effects

Question 12

What does it mean if OER = 1?

Answer 12

Means that Oxygen has no effect - like doesnt even have time to produce an effect; alpha

Question 13

What is OER at S phase vs. M phase?

Answer 13

2.8 at S, 2.3 at M. Obviously because at S its less sensitive

Question 14

Describe the relationship between OER and low/high LET radiations

Answer 14

OER is NOT seen at high LET - OER would be 1 (note that it cannot be 0). Not seen at high LET because there is no time for it to be seen. OER is seen much more at low LET!

Question 15

Why must oxygen be given microseconds after exposure for an effect to be produced?

Answer 15

because the half-life of the free radical is very small

Question 16

Describe what oxygen does; the basis of the theory; why does it make damage more?

Answer 16

Because it “fixes” the damge; i.e. it binds to the free radical making RO2; makes the damage permanent

Question 17

Does oxygen have effect on indirect or direct DNA damage? Explain

Answer 17

Only indirect as it “fixes” the damage - direct would be like alpha, it will just kill the cell straight away

Question 18

Percentages: Of Oxygen in air: for normal, dizziness and unconsciousness?

Answer 18

20%, 16%, 10%

Question 19

At what % of oxygen does the effect double?

Answer 19

0.5%

Question 20

Define Chronic and Acute hypoxia. Give examples

Answer 20

Acute is short term, chronic is over time. Acute like laying on your leg, chronic like tumours taking up all the oxygen of nearby normal cells

Question 21

How far can oxygen travel in tissue?

Answer 21

70microM

Question 22

What is necrosis?

Answer 22

The dead inside part of tumor; cos tumor took all the oxygen (70microM)

Question 23

Describe necrosis + tumor sheath

Answer 23

Sheath remains constant while necrosis grows. Necrosis seen at 200 microM, absent at 160 microM

Question 24

What happens with p53 and tumors?

Answer 24

p53 usually arrests mutant cells, but then it becomes a mutant itself so it doesnt arrest, tumor keeps growing as it is resistant to apoptosis

Question 25

Define Reoxygenation

Answer 25

Basis: Hypoxic cells within tumor obtain more oxygen as the cells around it die, so the enxt time they have higher OER = they die