proton

Question 1

source of protons for proton therapy

Answer 1

hydrogen as it only has protons (1)

Question 2

mass of proton

Answer 2

2000 times the mass of e-

Question 3

protons have high

Answer 3

inertia mass

which is the difficulty to accelerate an object in order to change object motion acceleration

Question 4

protons require

Answer 4

2000 times more force to get the same kind of deviation of e-

deviation =moving the beam direction

Question 5

features of protons

Answer 5

-lateral scatter is low as protons are not deflected by e
-some side scatter
-RBE=1.1
-proton loss per interaction is small
-secondary nuetrons and gammas are produced

Question 6

range of secondary e- is..

Answer 6

small tf secondary dose is all absorbed locally

Question 7

nuetronal contimation

Answer 7

occurs in very high energies

Question 8

what is bragg peak

Answer 8

radiation instantly disappears after “BP”.
TF surrounding normal tissues dint get exposed to radiation

Question 9

how does bragg peak occur

Answer 9

-velocity of protons ↓ as they go thru deeper in tissue,

• energy is lost from protons via non-ionsing attenutaion

Question 10

the probability of …

Answer 10

causing ionisation ↑ as velocity↓

tf when protons go further into body, they are more likely to ionize tf less energy , tf velocity↓

Question 11

native beam

Answer 11

-proton beam has a positive feedback effect
-peak is v high and narrow
-build up of dose is slower and lower
-tail off is virtually instantaneous

Question 12

native beam is only useful for tumour @

Answer 12

c.25cm depth
c.2cm thick

Question 13

modified beam:
any modified beam must fit 3 goals:

Answer 13

-maintain (spread out bragg peak) characteristics
-allow beam to treat wide area
-treat different depths in 1 field

Question 14

when to use

Answer 14

-isolated and hard to treat surgically regions
*eye
*tumours close to spinal cord
*h&n
*paediatrics

Question 15

proton source : H

Answer 15

-H gas obtained from electrolysis of water
-high voltage applied to h gas to strip e-, leaving protons suspended in magnetic field

the protons are magnetically guided into synchroton or cyclotron

Question 16

synchroton

Answer 16

small p linac used to create high en p and then these are injected into synchroton (which is a circular accelerator ring)

-varaiable en
-lower beam current than cyclo

Question 17

what happens in the synchroton

Answer 17

electromagnets accelerate p

Question 18

cyclotron

Answer 18

-fixed energy machine
-high en gives max depth
-lower en only achieved by en degraders

Question 19

proton relativity

Answer 19

p accel. up to2/3 speed of light

when accel. , they gain mass

tf inertia ↑ which opposes changes in motion

Question 20

beam shaping

Answer 20

uses thin penicl beam of high en protons

Question 21

2 ways of shaping beam to useful size

Answer 21

-passive scanner
-beam scanning

Question 22

tissue denisty

Answer 22

p is v sensitive to tissue denisty
-BP is clser to surface of pt if path goes thru bone
-BP is deeper if path goes thru lung

tf tx spots are at different depths for some beams

Question 23

disadvantages pt1

Answer 23

-very expensive
-↑ skin dose
-bending proton beams is v. difficult bc of high mass

Question 24

disadvantages pt2

Answer 24

-beam delivery is challengeing bc of v large gantry
-range uncertianity tf OAR less than 2cm may not be spared