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Microwave Electron Linear Accelerators

for Cancer Therapy

and Non-Destructive Testing:

History, Application & Theory

Mark Trail, ManagerMicrowave & 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?

Electron Gun (-25kV)

A high-Q, resonantly coupled, microwave circuit that accelerators electrons to many MeV

Standing Wave Microwave Circuit (3Ghz)

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1895: Roentgen discovered X-rays

Shortly thereafter folks discovered that radiation kills cells

It all started with Wilhelm Roentgen

Definition:

RADIOTHERAPY –

The therapeutic application of ionizing radiation

A Little History…

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More History…

Russell Varian

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

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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 192,200 breast

169,500 lung 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-InvasiveNon-Invasive

Eradicates tumors, stops cancer cell Eradicates tumors, stops cancer cell replication or relieves pain,replication or relieves pain,

Treats 50% of all cancer cases in USATreats 50% of all cancer cases in USA

Typically, ~15min treatments, delivered 5 Typically, ~15min treatments, delivered 5 day/wk over 6-8 wksday/wk over 6-8 wks

Treatment is Painless - like having an X-Treatment is Painless - like having an X-Ray takenRay taken

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Radiation Therapy Facts… (cont) Side effects usually temporary; Depending Side effects usually temporary; Depending

on treatment site, can include nausea, loss on treatment site, can include nausea, loss of energy & appetite.of energy & appetite.

Millions of patients have been treatedMillions of patients have been treated

~5000 Varian medical accelerators ~5000 Varian medical accelerators presently treating patients world-widepresently treating patients world-wide

We ship 2-3 machines a day from Palo Alto We ship 2-3 machines a day from Palo Alto and build ~1km of accelerators/yearand build ~1km of accelerators/year

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Modern Medical Linacs Generates High-Energy X-rays Generates High-Energy X-rays

and/or electrons for Therapyand/or electrons for Therapy

Rotates around the patient Rotates around the patient delivering radiation from delivering radiation from multiple beam angles multiple beam angles

Capable of Volumetric Cone-Capable of Volumetric Cone-Beam CT ImagingBeam CT Imaging

Work in special treatment Work in special treatment rooms with 7-ft thick wallsrooms with 7-ft thick walls

How Do They Work?

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Inside a Varian Medical Linac

electron linac

beam transpo

rt

beam shapin

g

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Treatment Planning…

Treatment is typically

“fractionated”

20 – 30 “fractions” in 4

to 6 weeks (outpatient)

Dose the tumor – spare healthy tissue & minimize exposure to critical structures.

GoalProcess: 1) Acquire CT and/or

PET Images

2) Plan treatment

3) Irradiate from different angles

4) Vary penetration by varying beam energy

5) Shape Beam to conform to tumor

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Accelerating the electrons - the “Guide” or

“Accelerator”

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Accelerator: Side-Coupled Standing-Wave Design

Varian core technology!

1.5 m

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First we bake at 450C. Then pull a

high-vacuum

(Vacion pump)

Operate at ~10-8 torr (remove 99.999999999% of the air)

Accelerator: Side-Coupled Standing-Wave Design

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Up to 5.5 Megawatts peak, 5 kilowatts average

Fill with high power RF at 3 GHz

Insert electrons

Accelerator: Side-Coupled Standing-Wave Design

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RF power input

Side cavities couple rf Resonant

cavities

Axial electric fields

electrons

Accelerator: Side-Coupled Standing-Wave Design

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Beam Transport: The Bend Magnet

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Bend MagnetDirects the beam from accelerator towards patient

Three 90 degree bends + drift spaces

Doubly Achromatic (achromatic & non-dispersive)

One-to-one imaging, radial and transverse

Energy slits limit the energy acceptance Beam is ~ 1.5 – 2 mm

diameter

accelerator

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Bend MagnetDirects 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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Tungsten blocks coarsely collimate the beam

Collimator or “Jaw” System

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Fine beam collimation

Because tumors don’t have corners

Irregularly shaped field 120 tungsten

“leaves”

Multi-Leaf Collimator

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Intensity Modulated RadioTherapyDynamic 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…

IMRT

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Very good for VAR stock price!

• 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

IMRT

Dynamic motion of the MLC leaves while the beam is on.

“Paints” irregular dose distribution

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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 Sterilization

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