Radiobiology 1

Question 1

What does radiology stand for?

Answer 1

Field of clinical and basic medical sciences

Question 2

What are characteristics of cancer cells?

Answer 2

• Large number of dividing cells
• Large, variable shaped nuclei
• Small cytoplasmic volume relative to nuclei
• Variation in cell size and shape

-Loss of normal specialised cells
Disorganised arrangement

-Poorly defined tumour boundary

Question 3

What are the two types of radiation?

Answer 3

Direct

Indirect

Question 4

What are the types of cell cycle?

Answer 4

G1-growth
S-DNA synthesis
G2-growth and preparation for mitosis
M-Mitosis

Question 5

What cell cycles are radioresistant?

Answer 5

S-phase and G1(open structure)

Question 6

What does plating efficiency mean?

Answer 6

The percentage of cells seeded that grow into colonies

Question 7

What is the surviving fraction?

Answer 7

estimates survival are obtained for a range of doses (Doesn’t distinguish mode of death)

Question 8

What does a cell survival curve?

Answer 8

Count of surviving of cells following irradiation at discrete intervals of dose

Question 9

What are low-linear transfer?

Answer 9

X-rays, gamma rays

Question 10

What are high LET?

Answer 10

Alpha, Beta particles

Question 11

What are the two cell survival curves?

Answer 11

Linear quadratic model

Multivariate model

Question 12

What are the radiation variables of the cell survival curve?

Answer 12

Particle size
Particle charge
Dose rate
Low or high LET

Question 13

What are the tissue variables of the cell survival curve?

Answer 13

Mitotic Rate
Cell cycle phase
Oxygenation

Question 14

What are the components of cell killing?

Answer 14

One proportional to dose (alpha) single radiation track

One proportional to the square of the dose (Beta) 2 track

Question 15

What does the LQ model dsplay?

Answer 15

Cell kill both for tumour control and normal tissue complications

Question 16

Whats the rule for surviving fraction?

Answer 16

SF=e-^(alphaD *+BD^2)

Question 17

What happens at low doses?

Answer 17

two chromosomes breaks are the consequence of single electron (Linear)

Question 18

What happens at high doses?

Answer 18

two chromosome breaks are a consequence of two electrons (Quadratic)

Question 19

What does the alpha/ beta ratio mean?

Answer 19

where linear and quadratic components are equal

Theoretical measure of a tissue’s predicted response to a dose of radiation

Question 20

What does a high alpha/beta ratio (10)?

Answer 20

• tumour response is less dependent on the radiation (most tumours)
• early responding tissue

Question 21

What does a low alpha/beta ratio (3)?

Answer 21

Large dose of radiation is required to provide improved efficacy in terms of tumour control
-Late responding tissues

Question 22

What are single and multi hits?

Answer 22

alpha and beta

Question 23

What are more radioresistant SCC or sarcoma cells?

Answer 23

SCC

Question 24

What does BED mean?

Answer 24

Means of comparing the effectiveness of different treatment regimens

Question 25

What is the BED equation?

Answer 25

E/A=(nd) (1+d/a/b)

Question 26

What are the benefits of Fractionation?

Answer 26

- Allows for sublethal repair of normal tissue - increases damage due to reoxygenation and reassortment of cells into radiosensitive phase - Excessive prolongation leads to cell proliferation

Question 27

What are the 5Rs of radiobiology?

Answer 27

Repair of sublethal damage - Reoxygenation of hypoxic tissue - Redistribution or reassortment - Repopulation or regeneration - Radiosensitivity ( Intrinsic)

Question 28

What are the three types of damage?

Answer 28

Lethal damage Sublethal damage Potentially Lethal damage

Question 29

How do normal tissues repair?

Answer 29

repair pathways Cell cycle arrest In normal p53 is inactivated by mdm2

Question 30

Do malignant cells repair?

Answer 30

No | often through mutation or inhibition of TP53 prevents repair

Question 31

What are the reassortment phase?

Answer 31

When a small dose is delivered over a short period cells will cycle through to more radiosenstive phases.

Question 32

What is repopulation phase?

Answer 32

Following irradiation some cells will exhibit increased cell division (quicker in NT)

Question 33

What is the reoxygenation phase?

Answer 33

Allow enough time to reoxygenise.

Question 34

What is radiosensitivity?

Answer 34

Different radiosensitivity in different cells radiosensitivity (gametes) radioresistant( melanoma and sarcoma)

Question 35

Is a high OER desirable?

Answer 35

Yes makes cells more sensitive to cell damage

Question 36

What is OER?

Answer 36

Hypoxic/Aerated

Question 37

What is the oxygen fixation hypothesis?

Answer 37

Damage produced by free radicals in DNA can be repaired but may be fixed "irreparable" if molecular oxygen is available (Forms an organic peroxide non restorable for target material)