MV beam

Question 1

what type of beam is MV?

Answer 1

heterogeneous

Question 2

what are the two main energies?

Answer 2

6MV and 10MV

Question 3

what is DMAX?

Answer 3

1/4 of the energy

Question 4

what is the interaction process

Answer 4

CS

Question 5

where is DMAX

Answer 5

100% is a few cm below the skin surface
100% is NEVER the skin surface

Question 6

what direction is the scatter

Answer 6

forward due to the narrow beam

Question 7

does MV have a higher proportion of scatter compared to KV

Answer 7

yes

Question 8

what is a feature of MV and NOT KV

Answer 8

skin sparing
all tissues drop off after 100%

Question 9

what is an isodose distribution?

Answer 9

the radiation path through the patient and the deposition through the body

Question 10

what happens to all the photons outside the CA

Answer 10

they will diverge

Question 11

what is the treatment beam the same as

Answer 11

the imaging beam

Question 12

why are low mv used

Answer 12

reduce scatter

Question 13

describe the resolution

Answer 13

poor resolution especially above 6MV

Question 14

what is the direction of scatter

Answer 14

forward

Question 15

why is contrast reduced

Answer 15

because CS is the main interaction process, all tissues have similar electron densities so all tissues look the same - dependent on the number of electrons in the absorbing material

Question 16

what is resolution

Answer 16

it is the amount of detail which an image holds

Question 17

what are the two attenuation processes

Answer 17

absorption: radiation dose
scatter: deflected radiation path which contributes to the absorbed dose

Question 18

describe contrast usage at high and low energies

Answer 18

at low energies the contrast in bone is higher, whereas at high energies the contrast is decreased. At high energies the contrast is similar for both bone and air