Topic 6: Linac

Question 1

5 main parts of the linac

Answer 1

drive stand
gantry
treatment couch
control console
modulator cabinet

Question 2

4 parts of the drive stand

Answer 2

kylstron or magnetron
waveguide
circulator
water cooling system

Question 3

function of the kylstron

Answer 3

amplifies microwaves

electrons are accelerated and then slowed and the loss of energy is transferred to microwaves

Question 4

function of magnetron

Answer 4

amplifies electrons
pulsed DC field accelerates electrons from cathode to anode
electrons spiral into cavity and release microwave energy

Question 5

where does energy go after microwave amplification

Answer 5

waveguide

Question 6

which is used in energies lower than 6MV magnetron or kylstron

Answer 6

magentron

Question 7

2 parts of the gantry

Answer 7

electron gun

waveguide

Question 8

function of electron gun

Answer 8

produces electrons and injects them into accelerator/waveguide structure

Question 9

function of waveguide

Answer 9

adjusts the speed of electrons - quickens slow e, slows fast e
electrons gain energy from the microwaves

Question 10

the _____ the accelerator structure, the greater the acceleration and greater the energy

Answer 10

longer

Question 11

what are some key differences between standing and travelling waveguides

Answer 11

standing - microwaves are reflected back towards the source by a mirror; coupling devices located on the sides

Question 12

what does the head of the gantry contain

Answer 12

bending magnet
xray target
scattering foil
flattening filter
dose monitoring systems
primary & secondary collimators
accessory tray

Question 13

function of bending magnet

Answer 13

bends electrons 270 degrees to interact with target (photon mode) or scattering foil (electron mode)

fyi - 3 ways to bend 90, 270 achromatic bending, 112.5 slalom bending

Question 14

what do primary collimators define

Answer 14

max field size

Question 15

what do secondary collimators define

Answer 15

field size in 4 dimensions bia asymmetric jaws

Question 16

function of scattering foils

Answer 16

only used for electron mode

scatter the electrons evenly across tx field

Question 17

function of dose monitoring system

Answer 17

measure radiation output

monitor field flattness and symmetry

Question 18

what does the dose monitoring system have to do with MUs

Answer 18

since there is a lack of uniformity of dose due to the clumping that occurs in the accelerator structure dose must be measured before releasing to the pt
these monitoring systems recognize a specific amount of ionization events as one monitor unit

Question 19

what is the function of the flattening filter

Answer 19

only with photon mode
placed in xray beam to reduce the intensity of the forward peaked dose in the centre of the field providing dose uniformity

Question 20

due to flattening filter horns occur, what do they represent?

Answer 20

preferential attenuation of low energy photons

Question 21

what is the main advantage when going FFF

Answer 21

dose rate increases

Question 22

what are the additional adjustments that 6D couches provided

Answer 22

yaw, pitch, roll

Question 23

what does the modulator cabinet contain

Answer 23

fan control,
auxiliary power distribution system (contains emergency off button),
primary power distribution