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ANOTHER TREATMENT

REVOLUTIONHelical TomoTherapytreatments are widely

accepted as the gold standard in radiation

treatment delivery. With the new Dose Control

System, Accuray Incorporated continues

to improve treatment quality and systemperformance. The Dose Control System

virtually eliminates dose rate variations during

each gantry rotation, treatment session, and

over the entire course of treatment. In particular,

dose rates during longer treatments such

as total marrow irradiation and stereotactic procedures will now remain within even more

tightly-controlled limits. Further, safety interlocks that interrupt a treatment because of dose

rate instabilities are dramatically reduced with DCS. A more consistent dose rate means fewer

system adjustments by staff and service personnel.

DCS KEY BENEFITSDCS MAINTAINS DOSE RATE CONSISTENCY

Throughout daily treatment delivery

Throughout a course of treatment

Between service visits

DOSE CONTROLSYSTEM (DCS)

TECHNOLOGYFeedback: Electron Gun Current

Feedback: Measured Dose

Dose ControlSystem

Inputs

Electrons ElectronGun

LinearAccelerator

(LINAC

)

Outputs

RF Power

X-Rays

ControlSoftware

DoseMonitor

DCS MINIMIZES SYSTEM INTERRUPTIONS

Due to rotational dose rate variation

Due to dose rate drift

DCS OPERATIONAL DIFFERENCE

Without DCS With DCS

System tuning is accomplished during a service

visit and remains constant between visits

An initial service procedure prepares the machine

for servo operationOutput variations naturally occur due to mechanical,thermal and component variations

A feedback system monitors gun currentand dose rate

Once dose levels are observed approachingtolerable limits, service intervention re-tunesthe machine

Near real-time control of RF power and gun currentis based on feedback signals

Greater mechanical, thermal, and componentvariations can be tolerated without intervention

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DCS EXAMPLESDose rate variation

In this example, the dose output without

DCS installed exhibits both a gradual

average drop over several minutes and a

rotational variation per gantry revolution.

The DCS system is able to stabilize both

the periodic and gradual dose variations

Interrupts

Examination of system log files can reveal the

rate of interrupts of various types. These include

interlocks due to deviations in actual dose rate

from the expected dose rate. Data analysis for

the 18 systems in a DCS pilot program shows tha

the weekly rate of these interlocks decreased

onaverage by approximately 90% between the

before DCS and with DCS data, or going fro

one dose rate-related interrupt every few days to

one every few weeks or months of clinical use.

DCS TECHNICAL ESSENTIALS DCS is a servo mechanism based on feedback from the monitor ionization chambers (dose output measurement)

and injector cabling (electron gun current measurement)

DCS controls magnetron power output and injector current to maintain constant dose output

and gun current

DCS is designed to stabilize both dose rate (via magnetron power) and beam energy (via gun current)

At the heart of the Dose Control System is a closed loop feedback process. The concept is simple: the system

continuously monitors key output signals in order to make small, rapid adjustments to the parameters that control

the beam. The result is consistent dose rate maintained by an intelligent feedback loop that constantly compensate

for factors such as mechanical motion due to gantry rotation, along with temperature shifts and component wear.

DCS CONTROL LOOPS

Pulse

C

ount

Output (Raw)

36000

35000

34000

33000

320000 1000 2000 3000 4000 5000 6000

Before Dose Control System

After Dose Control System

2012 Accuray Incorporated. All Rights Reserved. Accuray, the stylized logo, CyberKnife, Synchrony, Xsight, Xchange, RoboCouch, TomoTherapy, HiArt, and TomoHD are among the trademarks and/or registered trademarks of Accuray Incorporated

in the United States and other countries. TomoTherapy is a wholly owned subsidiary of Accuray.

500857.A

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Average dose rate errors per week

dose rate errors per week

before DCS

with DCS

Gun Servo Control

Monitored:Gun currentControlled:Injector current setting

Dose Servo Control

Monitored:Dose ionization chamber signalControlled:Magnetron power output

Gun Servo

Dose Servo

Inj_I

PAC

X-RAY X-RAY

Gun l

Dose 1

Toroid

IonChamber

Radiation

Generating

System