Transcript Trail

Microwave
Electron Linear Accelerators
for
Cancer Therapy
and
Non-Destructive Testing:
History, Application & Theory
Mark Trail, Manager
Microwave & Physics R&D
April 10, 2008
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What is a
Medical Linear
Accelerator?
A Medical Device designed to
deliver ionizing radiation to a tumor.
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What is an
Electron Linear
Accelerator?
A high-Q, resonantly
coupled, microwave
circuit that accelerators
electrons to many MeV
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Electron
Gun
(-25kV)
Standing
Wave
Microwave
Circuit (3Ghz)
A Little History…
It all started with Wilhelm Roentgen
 1895: Roentgen discovered X-rays
 Shortly thereafter folks discovered
that radiation kills cells
Definition:
RADIOTHERAPY –
The therapeutic application of
ionizing radiation
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More History…
Sigurd Varian
1948:
 Varian Associates Founded
1950:
 Sigurd Varian prepared proposal
for 10MeV Medical X-Ray Linac
1955:
 Dr. Henry Kaplan builds 1st 6MV
Medical Linac
1960:
 Varian Clinac-6 Treats Patients
Russell Varian
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1955: Dr. Henry Kaplan’s 1st 6MV Medical Linac
(Stanford Medical School)
1st retinoblastoma patient.
Vision intact at last check (1996)
photos copyright Radiology Centennial, Inc.
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1962: Henry Kaplan with Varian Clinac 6
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Cancer Facts…

In the USA,

Leading Cause of Death

40% of us in this room will be diagnosed with cancer

14% of us will be treated on a Varian Linac

1.25 million new cancer cases annually
 198,100 prostate
 169,500 lung


 192,200 breast
 135,400 colorectal
Men – if you live long enough you will get prostate cancer
Treatment Options
 Surgery, Chemotherapy, Radiation Therapy, or combination
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Radiation Therapy Facts…

Non-Invasive

Eradicates tumors, stops cancer cell
replication or relieves pain,

Treats 50% of all cancer cases in USA

Typically, ~15min treatments, delivered 5
day/wk over 6-8 wks

Treatment is Painless - like having an X-Ray
taken
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Radiation Therapy Facts…
(cont)

Side effects usually temporary; Depending
on treatment site, can include nausea, loss of
energy & appetite.

Millions of patients have been treated

~5000 Varian medical accelerators presently
treating patients world-wide

We ship 2-3 machines a day from Palo Alto
and build ~1km of accelerators/year
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Modern Medical Linacs

Generates High-Energy X-rays
and/or electrons for Therapy

Rotates around the patient
delivering radiation from
multiple beam angles

Capable of Volumetric ConeBeam CT Imaging

Work in special treatment rooms
with 7-ft thick walls
How Do They Work?
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Inside a Varian Medical Linac
beam
transport
electron
linac
beam
shaping
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Treatment Planning…
Process:
1)
Acquire CT and/or
PET Images
2)
Plan treatment
3)
Irradiate from
different angles
4)
5)
Goal
Dose the tumor – spare
healthy
tissue
&
minimize
Shape Beam to
conform to tumor
exposure to critical
structures.
Treatment is
Vary penetration by
varying beam energy
typically
“fractionated”
20 – 30
“fractions” in 4
to 6 weeks
(outpatient)
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Accelerating the electrons the “Guide” or “Accelerator”
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Accelerator:
Side-Coupled Standing-Wave Design
Varian core technology!
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Accelerator:
Side-Coupled Standing-Wave Design
First we bake at
450C. Then pull a
high-vacuum
(Vacion pump)
Operate at ~10-8 torr
(remove 99.999999999% of the air)
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Accelerator:
Side-Coupled Standing-Wave Design
Fill with high power RF at 3 GHz
Insert
electrons
Up to 5.5 Megawatts peak, 5 kilowatts average
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Accelerator:
Side-Coupled Standing-Wave Design
Side cavities
couple rf
Resonant cavities
electrons
Axial electric fields
RF power input
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Beam Transport: The Bend Magnet
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Bend Magnet
Directs the beam from accelerator towards patient
 Three 90 degree
bends + drift spaces
 Doubly Achromatic
(achromatic & nondispersive)
 One-to-one
imaging,
radial and
accelerator
transverse
 Energy slits limit the
energy acceptance
Beam is ~ 1.5 – 2 mm diameter
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Bend Magnet
Directs the beam from accelerator towards patient
 Beam is directed
onto a “target” to
make x-rays
 Or passes through
for electron
treatments
Up to ~ 1 kw of beam
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e- Scattering Foils & X-Ray Flattening Filters
Scatter e-beams
and flatten X-beams
to make uniform at
patient
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Ion Chamber
Monitor dose
delivered to
patient
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Collimate/Shape The Beam
Limit the extent
of the beam –
only treat tumor
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Collimator or “Jaw” System
 Tungsten
blocks
coarsely collimate
the beam
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Multi-Leaf Collimator
Fine beam
collimation
Because tumors don’t
have corners
Irregularly
shaped field
120 tungsten “leaves”
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IMRT
Intensity Modulated RadioTherapy
Dynamic motion of the MLC leaves while the beam is on.
“Paints” irregular dose distribution
 Improved dose distributions, better
sparing of normal tissues
 Treatment planning must optimize
many variables
 Improved efficacy of treatments
 Good for the patient and…
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IMRT
Dynamic motion of the MLC leaves while the beam is on.
“Paints” irregular dose distribution
• improved dose distributions,
better sparing of normal tissues
• treatment planning must
optimize many variables
• information management is
very important
• complex treatments – lots of
work for the physicist
Very good for VAR stock price!
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Security & Inspection Products
 Same technology as Medical Linacs
 Very different applications
 Primary business is Cargo Inspection
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Mobile
Cargo
Inspection
Systems
Linatron™
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Other Security and Inspection Applications:
• Mega-Voltage Computed Tomography (CT)
• Sterilization of Medical Disposables
• Food Irradiation (sterilize fruit flies or kill pathogens in food)
Picture
of
Steriliz
ation
Linatrons
Each Accelerator Delivers:
- 10 MeV electrons
- 15kWavg Beam Power
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Job Opportunities at Varian:
 Presently, 30 openings in USA for all
levels of engineers
 Complete list available at
www.varian.com
 Please take a Varian Brochure
Thanks for Your Attention
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