The document provides information on the history and components of a linear accelerator (LINAC) device. It discusses how the first LINAC was developed in the 1920s and the first ones used for radiation therapy in the 1950s. The major components of a LINAC include an electron gun, waveguide system, treatment head with collimation and imaging devices, as well as safety and control systems. LINACs use high-frequency electromagnetic waves to accelerate electrons and produce x-rays for radiation therapy treatments.

1. LINEAR ACCELERATOR
BY- PALLAVI JAIN
MODERATOR- ANKUR MOURYA SIR

2. HISTORY
• The first linear accelerator principle was invented
by Rolf Wideroe in 1928 to accelerate heavy ions
• In 1952, the first linear accelerator designed for
radiotherapy was installed at Hammersmith
hospital, London
• In 1956, the first patient was treated at Stanford
University in USA
A model of the 1953 8 MeV
linac installation at
Hammersmith Hospital.

3. LINAC
• Device that uses high-frequency electromagnetic waves to accelerate
charged particles such as electrons to high energies through a linear
tube using accelerator wave guide. It can be made to strike a target to
produce x-rays.

4. MAJOR COMPONENTS OF LINAC
• Power Supply
• Modulator
• Magnetron
• Electron Gun
• Wave Guide system
• Accelerator Tube
• Treatment Head
• Treatment Couch
• Control Console

5. A BLOCK DIAGRAM OF TYPICAL MEDICAL LINEAR
ACCELERATOR

6. TYPE OF SYSTEMS COMPONENTS
ELECTRON EJECTION SYSTEMS ELECTRON GUN
MICROWAVE SYSTEMS MAGNETRON OR KLYSTRON
POWER SUPPLY SYSTEMS MODULATOR CABINET
BEAM TRANSPORT SYSTEMS ACCELERATING WAVE GUIDE
AUXILLARY SYSTEMS VACCUM PUMP
,CIRCULATING COOLING WATER,
RF FREQUENCY TUBE, PRESSURIZED DIELECTRIC
GAS (for RF transmission), RF ISOLATOR OR
THYRATRON
SAFETY INTERLOCK SYSTEMS Both HARDWARE and SOFTWARE
systems
COMPUTER CONTROLLED FEEDBACK SYSTEM MONITOR CHAMBER, hardware position
, limiting micro-switchers
BEAM COLLIMETER/APPLICATOR SYSTEMS JAW COLLIMETERS, MLCS

7. DRIVE STAND
• It is large rectangular cabinet that is firmly
secured to the floor of the room
• Gantry rotates on horizontal axis in the
drive stand.
• Major components of the drive stand is:
1. Power supply
2. Modulator
3. Cooling system/ Water tank
4. Magnetron or klystron
DRIVE
STAND

8. POWER SUPPLY
• Provides DC current power to the
modulator which includes pulse
forming network
• High voltage pulses from modulator
section are flat topped DC pulses of
few microseconds in duration.

9. MODULATOR CABINET
• Contains three major subcomponents-
1. Fan control ( cooling the power distribution systems)
2. Primary power distribution systems (gives power to
machine)
3. Auxiliary power distribution systems. (emergency off
button to shut off power to treatment unit)
• Supplies pulsed power to magnetron and electron
gun when triggered by a timing pulse from control
console.

10. COOLING SYSTEM/ WATER TANK
• Locted in drive stand
• Provide thermal stability to the system
• Helps in maintaining a constant temperatures so that the components in drive
stand and gantry functions properly.
• Demineralized water is used for cooling.
• Normal water temperature is 20-30 C
• SF6 is used which acts as dielectric and thus prevent sparking.

11. MAGNETRON
• Device that produces microwaves
• Functions as a high-power oscillator, generating microwave
pulses of 3000MHz
• High voltage short duration pulses in synchrony with
electron gun is supplied to inner circular cathode which
result in thermo-ionic electron emission to outer anode in
presence of perpendicular magnetic field .This produces
microwaves.
Cross-sectional
diagram showing
principle of
magnetron
operation

12. KLYSTRON
• Klystron is not a generator of microwaves but rather a microwave amplifier
• It needs to be driven by a low-power microwave oscillator
Cross-sectional drawing of a two-cavity klystron

13. GANTRY
• It can rotate by 360
degree
• It is isocentrically
mounted
• C- Type
• It consist of :
• Electron gun
• Wave guide systems
• Treatment head

14. • The linac injection system is
the source of electrons,
referred to as the electron
gun
• Produced thermionically
• Injected onto the central
axis of the waveguide.
ELECTRON GUN

15. ELECTRON GUN
• It consist of:
• Cathode – negatively charged ,1 cm3 of barium
aluminate, produce electron by thermo-ionic
emission
• Gride / gate- switch like mechanism , consist of
copper screen
• Anode – positively charged , attracts electron,
perforated so that some electrons are passed into
accelerating wave guide

17. WAVE GUIDE SYSTEM
• Accelerating waveguide is obtained from a
cylindrical uniform waveguide by adding a series of
disks (irises) with circular holes at the centre, placed
at equal distances along the tube to form a series of
cavities
• The accelerating waveguide is evacuated to allow
free propagation of electrons.
• Often pressurized with dielectric freon or SF6 to
reduce possibility of electric breakdown and
increase power handling capacity.

18. TYPES OF ACCELERATING WAVEGUIDE
• Travelling wave structure : structures require a terminating, or
“dummy,” load to absorb the residual power at the end of the
structure, thus preventing a backward reflected wave.
• Standing wave structure: provide maximum reflection of the
waves at both ends of the structure so that the combination of
forward and reverse traveling waves will give rise to stationary
waves, more efficient than the traveling wave designs since axial,
beam transport cavities, and the side cavities can be
independently optimized

19. TREATMENT HEAD
• Bending magnet
• X-Ray Target – tungsten
• Primary Collimator
• Flattening Filter –to produce a “flat” beam
• Monitor Chambers – ion chamber
• Asymmetrical jaws- X and Y
• MLCs
• Shielding against leakage - tungsten, or lead–tungsten
alloy
• Light localizer system

20. BENDING MAGNET
• Projects the electron beam onto the
target.
• Produce different beam path for different
energies.
• Present in high energies linacs
• Two common bending magnets afe:
• 90 degree- chromatic deflection
• 270 degree- achromatic deflection
• 112.5 degree- slalom

21. X RAY TARGET
• Bremsstrahlung x-rays are produced when the electrons are incident on a target of a
high-Z material such as tungsten
• target is water cooled
• target is thick enough to absorb the incident electrons
• the electron energy is converted into a spectrum of x-ray energies
• maximum energy equal to the incident electron energy
• average photon energy of the beam is approximately one-third of the maximum
energy

22. THE ELECTRON BEAM
• It exits the window of accelerator tube , a narrow pencil of about
2mm in diameter
• This beam instead of striking the target ,is made to strike the on
electron scattering foil to spread the beam as well get a uniform
electron fluence across the treatment field.

23. Components of treatment head. A: X-ray therapy mode. B: Electron therapy mode

24. COLLIMATION SYSTEMS
• Limiting the radiation beam
• Beam modifying device
• Primary/fixed collimation
• Secondary/movable collimator
• Tertiary collimator

25. PRIMARY/FIXED COLLIMATION
• defines a maximum circular field
• one end of conical opening of the
collimator projecting onto edges of the
target and the other end to the flattening
filter
• Depleted uranium/Tungsten
• Transmission <0.2%

26. FLATTENING FILTER
• Conical metallic filter
• Situated between target and ion chamber
• Produce a uniform intensity distribution
• Usually made up of lead , steel or copper or
tungsten ,aluminum or uranium combinations
• Modifies the narrow non uniform photon beam
at the isocenter into clinically useful flattened
beam with uniformity and symmetry.

27. IONIZATION CHAMBER
• Transmission ionization
chambers consist of two
separately sealed ionization
chambers with completely
independent biasing power
supplies and readout
electrometers for increased
patient safety
• monitor dose rate, integrated
dose, and field symmetry

28. • Scattering foil –
• Thin , high Z foil(tungsten or lead or aluminium)
• In electron mode of linac
• Electron beam of 3 mm diameter instead of striking the target ,strike
this foil to produce uniform electron fluence across the treatment
• Carrousel-
• Helps in movement of flattening filters of different energies as well as
scattering foils

29. SECONDARY/MOVABLE COLLIMATOR
• After passing through the ion chambers, the beam is further collimated by a
continuously movable x-ray collimator
• consists of two pairs of lead or tungsten blocks (jaws) mounted on either side of
the central axis
• provide a rectangular opening from 0 × 0 to the maximum field size (40 × 40 cm2
or a little less) projected at a standard distance such as 100 cm from the x-ray
source
• Transmission <0.5%

30. MULTILEAF COLLIMATORS
• consists of a large number of collimating blocks or leaves
• driven automatically, independent of each other, to generate a field of
any shape
• consist of 60 to 80 pairs, independently driven
• leaves are made of tungsten alloy (density = 17.0 to 18.5 g/cm3)
• thickness of leaves along the beam direction - 6 cm to 7.5 cm
• primary x-ray transmission through the leaves - < 2%
• interleaf (between sides) transmission - > 3%
• thickness on inner leaves is 0.5 cm - 40 pairs, while its 1cm for the outer 20
pairs

31. TYPES OF MLC
Siemens - retain upper but
replaces lower Jaw
Elekta - retain lower jaw +
backup collimators, replaces
upper jaw
Varian - retain all jaws + MLC

32. BEAM LOCALIZATION
• The field size definition is provided by light localizing system in treatment head
• Consists of mirror & light source
• Located in space between chambers & jaws
• Provides an intense light field, duplicating in size & shape the radiation field
• Facilitates positioning of patient’s for treatment

33. AUXILIARY SERVICE
• Vacuum pumping system producing high vacuum in the accelerating waveguide
• Water cooling system for cooling the accelerating waveguide, target, circulator
and RF generator
• Shielding against leakage radiation produced by target, beam transport system
and RF generator

34. COUCH/ TREATMENT TABLE
• It is provided to support
the patient to be treated
• It is isocentrically mounted
as the Gantry & Collimator
• Made up of carbon fiber

35. Dynamic
Floor
In Room
Display
Lasers
Green laser- Silicon diode
2 sagittal , 1 coronal
Tolerance of laser position-
2mm

36. COUCH MOVEMENTS Can move horizontal,
vertical, lateral and
rotational directions.

37. HAND PENDANTS
• Contains all the control
switches which can used to
access the movement of
gantry , couch, collimeters ,
jaw, etc

38. CONTROL CONSOLE
• 4D integral treatment console
• Treatment console/service monitor : Provides status
information on treatment modality, accessories in use,
prescribed dose & dose delivered, interlock status,
emergency off
• ARIA information system : appointment scheduling
• ARIA is a comprehensive information system that
addresses the clinical, administrative, and imaging
needs of the oncology department. It provides a single
user interface that integrates record and verifies the
multileaf collimator, and PortalVision
Service
Monitor
ARIA Information
System
4D ITC

39. ELECTRONIC PORTAL IMAGING DEVICE(EPID)
• On board imaging
• MV Xray
• Real time imaging
• IGRT
• Flat panel amorphous silicon
• Detectors mounted on retractable arm
• 1024 * 768 resolutions

40. RADIATION SAFETY /INTERLOCK SYSTEMS
• Last man out(LMOS) switch
• Door interlock
• Beam on-off switch
• Emergency switches
• Safety lights( red, yellow, green)

41. EMERGENCY BUTTONS
• Total 7 in number
• Completely turn off the entire unit with single switch during emergency
situations.

42. AUDIO VISUAL MONITORS

43. TREATMENT PLANNING SYSTEM

44. After completion of the installation, a formal radiation protection
survey is carried out –
• measurement of head leakage
• area survey
• tests of interlocks
• warning lights
• emergency switches
• There are daily ,monthly and annual quality assessment carried
out for proper functioning of the LINAC.

45. THANK YOU