Radiation is delivered from a source Machines in External ...
Transcript of Radiation is delivered from a source Machines in External ...
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Machines in External
Beam Radiotherapy
(EBRT)
Dr. Anushree Punia
➢ EBRT – Radiation is delivered from a source
which is at a certain distance from the patient
Radiation Therapy Equipment
On the basis of radiation energy used EBRT can be
classified as follows:-
1. Grenz Therapy
2. Contact Therapy
3. Superficial Therapy
4. Orthovoltage Therapy
5. SuperVoltage Therapy
1. Grenz Therapy
➢ Has a very soft beam (<20kV).
Absorbed within the first 2 mm
of skin - does not penetrate
beneath the dermis.
➢ Used clinically for skin lesions
like Atopic Dermatitis,
Psoriasis, Lichen Planus, Acne
➢ 40-50 kV small focal spot, short SSD (~5
cm)
➢ Absorbed with 2 cm of tissue.
➢ used for endocavitary irradiation.
Selected Rectal, Oral Kaposi Sarcoma etc)
2. Contact Therapy
3. Superficial Therapy
➢ 50-150 kV. SSD: 15/20 cm.
➢ The beam energy penetrates only the top
surface layer of the skin
➢ Treatment option for skin tumors of 5.0 mm
depth including BCC, SCC or Kaposi’s
sarcoma.
Grenz
Superficial
4. Orthovoltage (Deep)
Therapy➢ 150 - 500 kV.
➢ Treatment fields used to be defined using detachable cones.
➢ The SSD was typically 50 cm.
➢ Not in 'clinical' use- high skin dose
5. Supervoltage Therapy➢ 500-1,000kV
➢ Due to the demand of treating deeper tumors these units were created.
➢ Since conventional power transformers were not suitable for high energy
units (>300kV) so for new machines resonant Transformers were created to
facilitate which step up the voltage in an efficient manner
6. Megavoltage Therapy
➢ X-rays beam of energy 1 MV or greater.
➢ Teletherapy – Co60
➢ Particle accelerators - A device that uses
electromagnetic fields to propel charged
particles to high speeds and to contain them in
well defined beams.
TYPES
- Van de Graaff generator
- Betatron
- Linear accelerator
Click icon to add pictureBryant Symons
radium "bomb"
at Westminster
Hospital,
London,
England, in the
1930s.
➢ Until 1951, all isotope machines produced were teleradium units
(radium bomb).
➢ The SSD was usually not greater than 10 cm in these machines.
➢ Major drawbacks of these machines were high risk of radiation hazard
due to radon gas leak produced as a by product, high cost of radium,
large self absorption, low γ ray constant and low output
➢ For telecaesium units the SSD is 20 - 40cm.
➢ They have not been very popular because of relatively low γ ray
constant and low specific activity.
Isotope Machines
Telecaesium Unit
with applicators
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➢ 60Co teletherapy unit invented by
H.E. Johns in Canada in the early
1950s
➢ The first two cobalt teletherapy units
were installed in Canada in 1951, at
the Saskatoon Cancer Clinic and the
Victoria Hospital, London Ontario.
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Cobalt MachinesCobalt Machine
COLLIMATOR
COUCH
BEAMSTOPPER
GANTRY HEAD MAIN FRAME
The main components of a
teletherapy machine are: ➢ a radioactive source
➢ a source housing, including beam collimator and source
movement mechanism;
➢ a gantry and stand
➢ a patient support assembly; and
➢ a machine console.
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Radionuclides have been used as source of γrays for teletherapy
Radium-226, Cesium-137, Cobalt-60
60Co has proved to be most suitable for external beam R/T
Higher possible specific activity
Greater radiation output
Higher average photon energy
RadionuclideHalf-Life
(Years)
γRay Energy
MeVSpecific Activity Achieved in
Practice (Ci/g)
Radium-226 (filtered by 0.5 mm Pt)
1622 0.83 (avg.) ~ 0.98
Cesium-137 30.0 0.66 ~ 50
Cobalt-60 5.26 1.17, 1.33 ~ 200
Source
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60Co Source
The overall diameter of
a 60Co source is 1 to 3 centimeters.
Consists of pellets of radioactive
60Co encased in multiple layers of welded metal to prevent contamination of the environment and to absorb β-particles produced by the decay process.
Or 60Co sources are made with the 60Co fused into a solid cylinder. Advantages:
Smaller source with less penumbra for the same beam intensity
Less hazard of contamination should a source
Typical source activity: of the order of 5 000
- 10 000 Ci
Typical dose rates at 80 cm from source: of
the order of 100 - 200 cGy/min
Teletherapy source is usually replaced within
one half-life after it is installed.
❑ methods for moving the source from OFF position to ON
position-
1. Source mounted on a rotating wheel inside the source
head to carry the source from OFF to On position
1. Source mounted on a heavy metal drawer is moved
horizontally by pneumatic system 3. Mercury is allowed to flow into a container immediately
below the source to shut OFF the beam.
4. Source is fixed in front of the aperture and the beam can
be turned ON and OFF by a shutter consisting of heavy metal
jaws.
Collimators➢ Collimators provide beams of desired shape and
size.
➢ Collimators of teletherapy machines provide
radiation fields typically ranging from 5 × 5 to 35
× 35 cm2 at 80 cm from the source.
➢ The rotational movement of the collimator is
continuous and it can rotate 360° about its own
axis.
Gantry
➢ The gantry can rotate by 360°.
➢ The rotational movement of the gantry is motorized
and controlled in two directions continuously; its
rotation speed can be adjusted.
➢ Teletherapy machines are most often mounted
isocentrically, allowing the beam to rotate about
the patient at a fixed SAD.
➢ They can be used either as fixed field machines or
rotation units.
➢ Modern teletherapy machines have SADs of 80
The axis of rotation of the three structures: Gantry, Collimator and Couch
coincide at a point known as the Isocenter.
Isocentric Mounting advantages:-
➢ Enhances accuracy.
➢ Allows faster setup and is more accurate than older non isocentrically
mounted machines.
➢ Makes setup transfer easy from the simulator to the treatment machine.
Isocenter
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Patient Support Assembly
Treatment Bed has horizontal, vertical and lateral
motorized movements
➢ Table Top - 90o rotation to each side
➢ Base - 110o rotation to each side
➢ Bedtop size l x w cm (in) - 235 x 46 (93x
18)
➢ Patient weight capacity kg (lb) - 136 (300)
Control Console
➢ Control Console is situated outside the bunker
➢ It consists of following:-
CONTROL PANEL - The control panel including following functions..Confirm
push button, Treat push button, Pause push button, Terminate push button,
Power on indicator, Inhibit indicator, Inhibit reset key, Power key switches,
Audible signal, Auto set up /motion enable push button, Remote gantry
positions
DISPLAY MONITOR - A display monitor displays system information such
as..Start up information, Treatment time, Wedge details, Field size and
collimator angle, Table parameters
Beam characteristics for 60Co
1. Depth of maximum dose = 0.5 cm
2. SSD = 80cm
3. Increased penetration (10-cm PDD = 55%)
4. Beam edge not as well defined—penumbra due to
source size
5. Dose outside beam low because most scattering is
in
forward direction
6. Isodose curvature increases as the field size
❑SAFETY &PROTECTIVE FEATURES
❑EMERGENCY SWITCHES
➢ The emergency switches when pressed this will
remove the power from the unit and table motion
drive circuit & also source goes to its fully shielded
position
They are located on
➢ Control console
➢ Main frame of machine
➢ Hand control
MACHINE
NAME 780 780 C ELITE 80 EQUINOX
FIELD SIZE Min:5X5;
Max:35X35
Min:5X5;
max35X35
Min:5X5
Max:35X35
Min:4X4
Max35X35
JAWS SYMMETRIC SYMMETRIC SYMMETRIC ASYMMETRIC
WEDGE 30o 45o
60o
Very rarely
used
30o 45o
60o
Very rarely
used
15o 30o
45o 60o
Max field
size:
15W x 20
For 60 :10W
x15
15o 30o 45o
60o
Max field size:
15W x 20
For 60: 10W x
15
BREAST CONE NO YES YES NO
TRIMMER YES NO No NO
BLOCK AP Y Y Y Y
PA Y Y Y NO
LATERAL NO Y Y NO
Bhabhatron - I
An Indigenous Teletherapy cobalt machine
developed in INDIA
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Bhabhatron - II Panacea Medical Technologies Pvt LTD
Bhabhatron - II
MAJOR FATURES :
Indigenous Teletherapy Machine
Low Cost
Battery backup
Enhanced Safety
Minimum Field Size at SAD : 3 x 3cm
Computerised motorized wedge
Asymmetric Collimator
Van de Graaff generator
Typically produces high
energy X-rays of 2MV
Can go upto 10MV but
limited by size and required
high-voltage insulation
No longer produced
commercially
Betatron
Principle- An electron in a
changing magnetic field
experiences acceleration in a
circular orbit
Can provide wide range of
energy from 6 MeV to 40 MeV
Dose rate and field size
capabilities of medical
betatrons are low compared
with LINACS and cobalt
machines
Betatron
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LINEAR ACCELERATOR
History 1948: A working 1MV linear accelerator was installed at the
Fermi Institute in Chicago.
1952: linac installed at Hammersmith Hospital in London.
1956: first clinically used in the US at the Stanford University
Hospital.
1961: The first 100 cm SAD fully isocentric linear accelerator
was manufactured and installed in the US
A 2-year-old boy suffering with
retinoblastoma was the first
patient to receive radiation from
the medical linear accelerator at
Stanford
History of LINAC in India
1976- 1st Linear accelerator set up in WIA Cancer Institute,Chennai
TMH got the 1st LA in 1980 –Mevatron 12.
1982 TMH got Clinac 6.
1994- 1st Dual energy LA 2100 C.
1999- 2nd dual energy LA 2100 CD.
2003- Single energy 6EX.
2005- Primus Dual Energy LINAC (ACTREC)
2007- Tomotherapy (ACTREC)
2009- Trilogy and Tomotherapy
2011- Novalis
Accelerator Generations
Early Accelerators (1953-1961):
Extremely large and bulky
Limited gantry motion
Second Generations (1962-1982):
360 degree rotational
Allow treatment to a patent from any gantry angle
Improvement in accuracy and dose delivery
Third generation accelerators:
Improved accelerator guide
Magnet systems
Beam-modifying systems to provide wide ranges of beam energy, dose rate, field size
First is the Power Supply which supplies power to
the modulator → Next comes magnetron or klystron
These devices convert the pulsed DC power into
microwave radiation that is supplied to the
Accelerator tube.
The modulator also supplies a signal to electron gun
which supplies the electrons to the accelerator
tube on command from the Modulator
Next is the wave guide system, these are copper
tubes that are used to efficiently transport
microwave energy from the magnetron or klystron
to the accelerator tube.
Basic Mechanism of LA
POWER
SUPPLYMODULATOR
MAGNETRON
OR
KLYSTRON
ELECTRON
GUN
Wave
Guide
System
Modulator
Power supply that converts AC to DC pulse forming network to
modulate current into pulses.
Pulse Forming Network(PFN) & Hydrogen Thyraton provide DC in
pulses.
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Thyratron
Gas-filled multielement tube
fabricated with glass or ceramic
tubes, metallic anodes, and one
or more grids.
Filled with hydrogen or
deuterium at low pressure.
Thyratrons are capable of
switching at rates greater than
20 kHz
The Magnetron
The cathode is heated by an inner
filament
Electrons are generated
by thermionic emission
Static M-field perpendicular to the plane of cavities
Electron move in complex spirals toward the resonant
cavities
Radiating energy in form of
microwave frequency of which is
about 3000MHz
Pulse E-field between cathode & anode
Electron accelerated toward the anode
The Klystron
Not a generator of microwaves
Microwave amplifier
Needs to be driven by a low-power microwave oscillator
The Klystron
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Electrons produced by the cathode
Electrons are accelerated by –ve pulse into buncher cavity
Lower level microwave set up an alternating E field across the buncher cavity
Velocity of e- is altered by the action of E-field (velocity modulation)
1. Some e- are speed up2. Other are slowed down
Passed in the drift
tube (field-free
space)
Electrons arrive catcher cavity
1. Generate a retarding E-field
2. Electrons suffer deceleration
3. KE of electrons converted into high-power microwaves
ACCELERATING WAVEGUIDE
The simplest kind of accelerating waveguide
is obtained from a cylindrical uniform
waveguide by adding a series of discs (irises)
with circular holes at the centre, placed at
equal distances along the tube.
These discs divide the waveguide into a
series of cylindrical cavities that form the
basic structure of the accelerating waveguide
in a linac.
Two types of accelerating waveguide have
been developed for the acceleration of
electrons:
TRAVELLING WAVEGUIDES
These guides have relatively low shunt
impedances compared to standing waveguide
systems therefore, they need to be physically
longer to achieve the same output energy.
Electrons from the gun end enter a velocity
of 0.8 c (at 80 kV) where c is the velocity of
light. After the first 30 cm, they are
travelling at velocities close to c.
This first part of the guide is called the
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Travelling wave guide
Riding the WavesAccelerators speed up charged particles by creating large electric fields
which attract or repel the particles. This field is then moved down the
accelerator, "pushing" the particles along.
Standing wave structure
In the standing wave structure each end of
the accelerating waveguide is terminated
with a conducting disc to reflect the
microwave power, resulting in a buildup of
standing waves in the waveguide.
In this configuration, at all times, every
second cavity carries no electric field and
thus produces no energy gain for the
electrons.
These cavities therefore serve only as
coupling cavities and can be moved out to
the side of the waveguide structure,
effectively shortening the accelerating
waveguide by 50%.
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Electron beam transport
In low energy linacs the target is embedded
in the accelerating waveguide and no beam
transport between the accelerating
waveguide and target is required.
Bending magnets are used in linacs operating
at energies above 6 MeV, where the
accelerating waveguides are too long for
straight-through mounting.
axis and the electron beam must be bent to
make it strike the X ray target or be able to exit
through the beam exit window.
● 90º bending (chromatic)
● 270º bending (achromatic);
● 112.5º (slalom) bending
Bending Magnet
Bending magnet: bends the electron beam through a right angle, so it ends up pointed at the patient
90 degree magnets (chromatic) have the property that any energy spread results in spatial dispersion of the beam.
Electrons are bent in proportion with their energy, the lower energy electrons are bent more, the higher energy electrons less
Results in a beam that is spread from side to side according to energy
Energy sensitive, act as energy differentiators
A 270o Magnet Using Hyperbolic
Pole Faces
more energetic electrons (larger radii) enter
closer spaced regions with higher bending
fields, and less energetic electrons encounter
lower bending fields between the wider pole
spaces.
all electrons that entered on axis at 0o
should converge again at the same point at
2700. The deflection is without dispersion
with energy (i.e. achromatic).
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Slalom Bending
➢used by Elekta (112.5 degree bend
➢solves energy dispersion and isocentric height problems
➢comprises three magnets: 2 at 45 degrees, one at 112.5
➢can focus to 2mm spot
Treatment Head
Linac in the photon mode –
start with the tungsten target
After the target will come the
primary fixed collimators which
determine the maximum extent of
the radiation field.
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There are 2 ion chambers in the
machine, one is used for backup in
case the other fails.
Radiation Output monitoring
Flatness and Symmetry monitoring
Sealed (reading independent of
temperature and pressure)
Same chamber for both photons
and electrons
It is the charge collected by the
chambers that
is used to shut down the machine
SCATTERING FOIL
A device to widen the thin pencil beam (3 mm) of electrons.
Metallic plates of tin, lead or aluminium are used.
Beam collimation can be improved by the use of dual foil system where the 1st filter spreads the beam out and the 2nd makes the dose homogenous by flattening are used.
Primary foil
Secondary foil
Electron
cone
Electron cone
Electrons readily interact with
the atmospheric air.
scattering of electron and beam
energy dissipation.
beam defining collimator with
variety of field sizes.
Secondary collimation close to
the patient’s body.
MLCs Type A
The Y jaws are replaced by bank
of MLCs.
Small traveling range of leaves
Shorter leaf length & compact
head diameter.
Used by Elekta
MLCs type B
The lower jaws i.e. X jaws are
replaced with bank of MLCs.
Used by Siemens
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MLCs Type C
MLC placed just below standard
upper & lower jaws.
Tolerance on leaf positioning &
leaf dimension is relaxed.
collimator will have over bulk.
Treatment Head & patient
clearance is considerably
reduced.
Used by Varian
Auxiliary system
The linac
auxiliary
systems:
Photo of Tomotherapy Unit with covers
removed
Forward Planning : Physicist specify Beams weights, Wedge angles, beam modifiers. They have direct control over these parameters at any point in the treatment planning process.
Inverse planning : Physicist does not specify these parameters. The numbers, energy & direction of the beams are still chosen by the physicist. But once beams have been specified, the computer takes complete control over all parameters e.g.MUs, weights, beam modifiers etc.
Item 2100CD 2100C Clinac 6EX
Photon Energy 6 MV, 15 MV 6MV, 10 MV 6 MV
Electron 6,9,12,15, 18MeV 6,9,12,16,20MeV X
Wedges Dynamic wedge option “ “
Field Size( with
wedges)
Max: 40x40cms
Min .5x.5
“
“
“
“
Dose Rate 100-600 MU/Min 80-400 100-600
Wedges 15,30 Steel
Rest Lead
15, 30 Steel
Rest Lead
15, 30Steel
Rest Lead
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Trilogy Novalis Tomotherapy
Wave guide Standing Standing Standing
Length 140cm 140cm 140cm
Rf power source
Klystron Klystron Magnetron
Rf frequency 3000Mhz 3000Mhz 3000Mhz
Field size Min-0.5 x 0.5Max-40 x 40cm
Min-0.5 x 0.5Max-40 x 40cm
Min-40 x 1cmMax-40 x 5cm
Jaws Asymmetric Asymmetric Symmetric
MLC 120(60 pairs) 120(60 pairs) 64 binary
Wedges 15,30 Steel 15,30 steel NA
COBALT LA
DOSE RATE Decreases constant
Energy source
diameter(penumbr
a)
high less
Source change 12,000 curie source= 35
lakhs
none
PDD at 10cm 55% 67%
Minimum field size 5x5cm 0.5x0.5 cm
Motorized wedges Not possible possible
Asymmetric jaws Absent present
COBALT LA
Source disposal Major problem nill
Cost of machine 1.9 crores 3 crores
True beam
Product of Varian
Flattening filter free
X ray(MV) – 4,6,8,10,15,18,20
Electrons (MeV) –
6,9,12,15,16,18,20,22
Max dose rate – 1000MU/min
Millenium 120 leaf MLC,
Max field size – 40 x 40cm
OBI -KV CBCT
Cyclotron
- Used as source of high energy
protons/neutron
-Consist of 2 electromagnets
-Hollow copper D
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LINAC CYCLOTRON
Large space requirement (few hundred m
long) but lightCompact but heavy
Expensive Cheaper in construction
Less efficient power conversion More efficient power conversion
Upgradable in energy Difficult to upgrade in energy
Straightforward beam extraction Difficult extraction and related beam losses
Capable of high beam current (100 mA) Modest beam current capability (5 mA)
Synchrotron
IN CYCLOTRON-As momentum and energy increase and the velocity of a particle approaches that of light, then the velocity begins to increase less rapidly than the particle mass, so the revolution frequency drops so that particles are no longer synchronous with the accelerating potential.
- IN SYNCHROTRON
A short pulse of particles is injected at low magnetic field, the field rises in proportion to the momentum of particles as they are accelerated and this ensures that the radius of the orbit remains constant.
The accelerated particles take less and less time to complete their orbit so the frequency of the accelerating alternative current must increase as well.
Synchrotron
Notice:
particles
travel in
a
ring, not
a disk
GAMMA KNIFE
1951 - Lars Leksell introduced the concept of
radiosurgery
System basically consists of the radiation unit
with the patient couch and collimator helmet,
the control panel and auxiliary systems.
Radiation System
▪ 201 cobalt-60 sources arranged in a hemispherical
pattern
▪ Each source is mounted at the head of a collimator
channel
which guides the radiation from the source to the focus
point
▪ Total activity of approximately 2.22x1014 Bq.
Shield assembly sources are heavily shielded within a cast iron body with
shielding doors
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CyberKnife Robotic Radiosurgery
System
Continuous feedback
Automated system
Detects any movement in tumor
or patient location
Corrects to ensure sub-millimeter
accuracy
Clinical Benefits
Staged/Fractionated Radiosurgery
1-5 fractions/stages
Larger lesions
Lesions next to critical structures/organs at risk
Improved Patient Quality of Life
Short treatment course: 1-5 days CyberKnife vs. 6-8 wks
Radiotherapy
Optimal for patients
Optimal for patients with limited life expectancy
Increased convenience
No infection risk
THANK
YOU
Dr Ashutosh
Dr
Carthikeyan
Dr Jatin