RAD03-2003- What happens when X-rays hit you or the patient?

Question 1

What is the photoelectric effect?

Answer 1

An X-ray photon collides with inner shell electron
This electron is ejected and another electron from an outer shell drops in to restore stability
This continues until a free electron is accepted
The X-ray photon has used all their energy and is absorbed
This energy is given off as heat or light

Question 2

What is the probability of photoelectric interaction occuring proportional to?

Answer 2

To Z cubed

Question 3

What is the Z for soft tissue?

Answer 3

7

Question 4

What is the Z for bone?

Answer 4

12

Question 5

How does increased density affect the number of bound inner shell electron increases?

Answer 5

As density increase, the number of bound inner electrons increases, so there is more chance of photoelectric effect to happen as more inner shell electrons could be hit

Question 6

Why does more absorption occur at lower kV?

Answer 6

Photoelectric interaction is inversely proportional to photon energy cubed (1/kV cubed)

Question 7

What is the overall result of photoelectric effect?

Answer 7

ionisation of tissues

Question 8

Why is there less absorption in soft tissues than bone?

Answer 8

343 is much less than 1728

Question 9

What is the absorption and scatter-Compton effect?

Answer 9

An incoming photon collides with an outer shell electron
This electron is ejected and replaced with a free electron
Photon hasn’t lost all energy so is deflected or scattered either into tissues or out of patient

Question 10

What is the overall effect of the Compton effect?

Answer 10

Ionisation

Question 11

What are the similarities between Compton and photoelectric effect?

Answer 11

an electron has been ejected

In photoelectric it is in the inner shell and in Compton it is in the outer shell

Question 12

How do X-rays cause direct damage?

Answer 12

X-ray photons interact directly with and ionise biological molecules such as: DNA, RNA, proteins and enzymes
This results in the breakage of macromolecule’s chemical bonds, which may in turn lead to inappropriate chemical reactions or cell death

Question 13

What is the result in bonds between nucleic acid breaking called?

Answer 13

Point mutation

Question 14

What occurs in somatic cells if nucleic acid bonds break and re-join abnormally and cells divide?

Answer 14

Give rise to Radiation induced malignancy

Question 15

What occurs in genetic cells if nucleic acid bonds break and re-join abnormally and cells divide?

Answer 15

Give rise to a congenital abnormality

Question 16

What subsequent events could occur after DNA damage?

Answer 16

Cell death, abnormal replication, only temporary damage so the DNA is repaired before further cell division

Question 17

What factors affect what occurs in the cell after photon exposure?

Answer 17

Type and number of nucleic acid bonds that are broken
Intensity and type of radiation
Time between exposures
Ability of cell to repair damage
Stage of cell’s reproductive cycle when irradiated

Question 18

How do X-rays cause indirect damage ?

Answer 18

X-ray photons ionise water molecule which produce ions and free radicals that can combine to form toxic substances which damage DNA

Question 19

What free radicals are formed from water ionisation?

Answer 19

H and OH

Question 20

What harmful substances can form from water free radicals?

Answer 20

Hydrogen peroxide

Hydroperoxyl radical