x-ray generator

Question 1

when were x-rays discovered

Answer 1

1895

Question 2

who discovered x- rays

Answer 2

Roentgen

Question 3

two different mechanisms by which x-rays are produced

Answer 3

bremsstrahlung x-rays and characteristic x-rays

Question 4

process of braking radiation as a result of a radioactive collision between a high speed electron and a nucleus

Answer 4

bremsstrahlung x-rays

Question 5

how does bremsstrahlung mechanism produce x-rays

Answer 5

as electron passes in vicinity of a nucleus, it suffers sudden deflection, the loss in energy is radiated as electromagnetic radiation.

energies are continuous

get photon as a result

Question 6

result of bremsstrahlung interactions in terms of energy

Answer 6

complete loss of energy or partial loss of energy

the resulting photon may have up to, but not exceeding the energy of the incident electron

Question 7

electron interacts by ejecting an orbital electron such as K, L, or M electron

Answer 7

characteristic x-rays

Question 8

result of characteristic x-rays in terms of energy

Answer 8

energies are discrete or specific

original electron continues with an energy equals to its initial energy minus energy given to the orbital electron

Question 9

Kilovoltage units

Answer 9

Grenz- ray therapy
Contact therapy
Superficial therapy
Orthovoltage therapy
Supervoltage therapy

Question 10

negative electrode

Answer 10

cathode

Question 11

consists of a wire filament, a circuit for current, and a negatively charged focusing cup

Answer 11

cathode

Question 12

when heated, emits electron by thermionic emission

Answer 12

tungsten filament

Question 13

tungsten filament’s purpose

Answer 13

heats up to emit electrons by thermionic emission

Question 14

cathode cup

Answer 14

directs electron from cathode to anode so that they strike the target in a well defined area, the focal spot

Question 15

positive electrode

Answer 15

the anode

Question 16

consists of thick copper rod at the end

Answer 16

the anode

Question 17

the tungsten target consists of

Answer 17

thick copper rod

Question 18

why is the tungsten used as the target material

Answer 18

because of high Z and high melting point

Question 19

what is the anode consist of

Answer 19

thick copper

Question 20

what is the cathode consist of

Answer 20

wire filament, a circuit, and a negatively charged focusing cup (to direct electron from cathode to anode)

Question 21

anode hood

Answer 21

prevents stray electrons from striking non target tube components

Question 22

Beryllium window and thin glass window

Answer 22

absorbs some of photon/x-rays

also called inherent filter

Question 23

the focal spot

Answer 23

small for diagnostic x-rays and larger for therapy x-ray tube

Question 24

removal of heat

Answer 24

achieved by circulating oil, water, air, rotating the anode in diagnostic x-ray

Question 25

X-ray tube efficiency

Answer 25

ratio of output energy emitted as X-ray to input energy deposited by electrons

Question 26

efficiency equation

Answer 26

9x10^-10 ZV

Question 27

what happens to the rest of the energy

Answer 27

converts to heat

Question 28

efficiency depends on what quantities

Answer 28

output energy x- rays and input energy electrons

Question 29

what are the specifications of quality of x-ray beam

Answer 29

quality of the beam in the range of kvp is specified in terms of energy and half value layer

Question 30

what is half value layer

Answer 30

the thickness of an absorber of specific composition required to attenuate the intensity of radiation to half of its original value under the condition of good geometry

Question 31

average energy

Answer 31

1/3 of the maximum energy of kVp

Question 32

x-ray energy spectrum for bremsstrahlung (unfiltered)

Answer 32

a continuous distribution of energies for photons

Question 33

what is the purpose of added filtration

Answer 33

enriches the beam with higher energy photons by absorbing the lower energy spectrum components

Question 34

x-ray energy distribution for characteristic x-rays

Answer 34

individual discrete energies

Question 35

where is added filtration placed

Answer 35

externally to the tube, further modifies the spectrum

Question 36

relationship between added filtration and beams

Answer 36

as filtration increases, x-ray beams hardens, which leads to achievement of higher average energy, therefore leads to greater penetrating power

Question 37

inherent filtration

Answer 37

absorption of low energy photons in the target, glass walls of tube, or thin beryllium window

Question 38

what is a LINAC

Answer 38

a device that uses high frequency electromagnetic waves to accelerate charged particles such as electron to high energies through a linear tube

Question 39

electron gun (LINAC)

Answer 39

filament when heated by an electrical current, releases electrons into the space around it

Question 40

accelerator guide (LINAC)

Answer 40

energized by microwave power mounted horizontally for high energies mounted vertically for low energies

Question 41

circulator (LINAC)

Answer 41

prevents any microwaves from returning to the Klystron- acts like valves in veins

Question 42

Water Cooling System

Answer 42

allows components in the drive stand and gantry to operate at a constant temp by circulating water

Question 43

Microwave system magnetron

Answer 43

magnetron is a device that produces microwaves

Question 44

Klystron

Answer 44

is a microwave amplifier, not generator- driven by a low power microwave oscillator

Question 45

pros of klystron

Answer 45

higher power microwave applications due to: 1. excellent stability 2. load isolation 3. high gain

Question 46

using E/M waves to accelerate electron

Answer 46

an electron will traverse a distance = 1/2 lambda in the time =1/2 period, accelerates continuously by the standing wave

Question 47

what is the function of a bending magnet

Answer 47

treatment units with a nominal90 degree or 270 degree beam bending magnet (mounted horizontally in the gantry) to redirect beam and select energy spectrum

Question 48

effects of bending magnet

Answer 48

spread of energy of the actual beam | spread of focal point at the x-ray target

Question 49

3 pole 270 bending magnet

Answer 49

limit energy spectrum exiting the magnet | refocuses electrons of correct energy

Question 50

LINAC treatment head

Answer 50

1. primary collimator 2. beam flattening system (flattening filter, scattering foil) 3. Dosimetry monitoring system 4. Moveable collimators

Question 51

beam collimation in x-ray mode

Answer 51

treatment field size is defined by the secondary collimator

Question 52

beam collimation in electron mode

Answer 52

must be achieved close to the skin surface of the patient due to their readily scatter in air

Question 53

beam flattening

Answer 53

produce a beam of uniform intensity

Question 54

flattening filter is for

Answer 54

x-rays

Question 55

scanning system or scattering foil is for

Answer 55

electrons

Question 56

what happens if flattening filter is removed

Answer 56

1. non uniform beam profile (highest intensity at center) 2. increase in dose rate, decrease in treatment time 3. softening of x-ray beam (increases surface, skin dose, shift dmax toward surface) 4. reduction in head scattered radiation 5. less neutron production due to higher dose per MU

Question 57

Flattening Filter Free (FFF) applications

Answer 57

``` small fields (SRS) IMRT ```

Question 58

purpose of FFF

Answer 58

1. higher dose rate 2. short term treatment as an advantage in motion management, patient comfort, treatment accuracy, reduce patient and target motion 3. beneficial for small fields and IMRT

Question 59

Scattering system

Answer 59

1. most common for flattening method 2. 1 or 2 metal foils are placed in beam to scatter electrons, results in spreading and flattening beam 3. produces x-ray contamination of the electron beam 4. initial alignment involves more mechanical adjustments 5. components are small and cheap

Question 60

Scanning system

Answer 60

1. a set of electromagnetic coils are placed around the beam 2. current to the coils vary in time, beam is bent such that it sweeps the field 3. relies on precise control of electromagnets 4. more expensive 5. if scanning fails and beam remains pencil beam for a long time, a high dose may be delivered to a very small volume

Question 61

Dosimetry Monitor

Answer 61

monitor dose rate, integrated dose, field flatness and symmetry

Question 62

Secondary blocking

Answer 62

after passing through ion chambers, beam is further collimated by continuously moveable X-ray collimator (produce rectangular field sizes)

Question 63

Teletherapy

Answer 63

external beam treatment in which source of radiation (gamma emitter) is at a large distance from patient

Question 64

Trimmers

Answer 64

metal bars extend downward from collimators to trim penumbra near the treatment surface by attenuating the edge of the beam, place no closer than 15 cm

Question 65

Transmission penumbra happens if the edges of the block are parallel with the central axis of the beam

Answer 65

true