Siriraj Radiation Oncolgy

Lalida TuntipumiamornDivision of Radiation Oncology

Department of Radiology,Faculty of Medicine, Siriraj Hospital

MAHIDOL UNIVERSITY

TomoTherapy

Scope of Talking

Overview of TomotherapyTomotherapy ProcessClinical ApplicationConcerned IssuesFuture Direction

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Acknowledgement

• Some of materials provided by -Timothy Holmes- PhD : St Agnes Cancer Center, Baltimore MD-Thomas Rockwell Mackie – PhD :

U of Wisconsin and TomoTherapy Inc.- Chester Ramsey-PhD : Thompson Cancer Center, Tenessee , USA

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To Get the Satisfied Dose Distribution

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Cone Beam Non-uniform Intensities with the Conventional Linac plus MLC

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-Limited Number of Beams and Directions

-Limited Number of Field Segmentations

Limited Degree of Intensity Level

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Fan Beam Intensity Modulation

• Common Name : Slice Therapy or Tomotherapy- Sequential /Serial

Tomotherapy- Helical Tomotherapy

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1994

Conventional Linear Accelerator added with Special MLC + Couch Control

Serial Tomotherapy : Peacock TM system

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Indexing and couch immobilization device

( CRANE)

Binary MLC MIMiC: NOMOS

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Maximum Field Size 2 x 20 OR 4 X 20 cm2

Serious Problem in Serial Tomotherapy!

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Over or under dose

Couch Indexing Error of as little as 1 mm can increase the total non-

uniformity to as much as 25%

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The New IMRT Delivery with Helical Tomotherapy …….

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Thomas Rockwell Mackie13

Concept for Helical Tomotherapy : Since 1993

CT ring gantry would be ideal for Tomotherapy with the modulated slit

beam using the bank of fast moving

collimators

Spiral delivery should improve the hot-spot or cold spot problem

at the junction

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Helical Tomotherapy is a Fusion of a Radiation Therapy Linear Accelerator

and a Helical CT Scanner

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Linac is mounted on a slip ring that allow continuous rotation around the patient (15-60 sec)

Independent Primary Jaws in the Superior-

Inferior Direction

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TOMO Binary MLC

Optical sensors and pneumatic driven

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MLC Characteristic

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51 projections/ revolution

Increase Degree of Freedom

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Megavoltage CT Imaging Capability

Capability of obtaining a CT , before , after or even during the

treatment will be possible

CT Image

detecto

r

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TOMO Beam Characteristic

Lack of the Flattening Filter -No scatter caused outside the field

- High dose rate

3.5 MV Low Dose Source (20 MU/min, 1.5 mm

point source)

Helical Tomotherapy Geometry

6 MV High Dose Source (860 MU/min, 1.5 mm

point source)

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Tomo Beam Characteristic Conical –shaped Profile

Lateral Profile

Radial Profile

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Low penumbra

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5 x5 cm Field Size

Dose at Depth More Uniform

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MVCT Image Guidance

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MVCT Imaging QualityHigh contrast resolution

= 1.2-1.6 mmLow Contrast resolution =

2-4%

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Don’t Forget for the MVCT Number to Electron Density

Conversion Table 32

TomoTherpy ProcessHelical Tomotherapy Process

• Imaging / Contouring• Planning / Optimizing• In-room Megavoltage CT Imaging• Image Registration ( IGRT )• Treatment Verification• Treatment Delivery

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Create ROI Optimization

Set initial value s for Importance and Penalty

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Dose Delivery Capabilities

Using maximum likelihood Estimator

Optimization

Spinal cord

U-shaped tumor

Total 91,800 pencil beam were used in

the optimization

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Planned Fluence Sinogram in Tomotherapy

2D array of energy fluence that corrleate between the projection and intensities

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Leaf Control Sinogram Corrected

tongue & groove , thread time

Planned Fluence SinogramFrom optimization process

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Plan QA

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IGRT

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Total delivery time ≅ 30 minutes

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TomoTherapy vs.

Clinical Application

Only single , 6 MV Photon Beam ?No Electron Beam ?

Coplanar Only ?IMRT Only?

Dosimetric/Clinical Advantage ?How about Integral Dose?

Questions

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Dosimetric gain in CI and HI of PTV and sparing of OARs was significantly obtained in HT vs. Conventional IMRT

But clinical advantage needs furthur investigation

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HT prostate planning generally provided treatment plans with excellent target homogeneity and

favorable critical structure sparing when compared to conventional IMRT

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Prostate , Vertebral –body retreatment = PTV Coverage + Sparing OAR , HT = Linac

Pediatric ethmoid sacroma retreatment =PTV Coverage both OK , but HT show a little bit better sparing OAR

Subtle dosimetric difference But no marked advantage with either system

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SRS Capability

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Helical Tomo shows larger lower isodose line volumes, longer treatment time , and can treat

a much larger lesion than Gamma-knife

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Dosimetric Advantage from Tomo but Integral Dose

increase 6.5 %

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TomoTherapy Integral Dose!!

A Potential Risk Factor for Secondary Cancer ?

Integral Dose = Mean Dose x Volume

636 MV 3DCRT 6 MV IMRT TOMO IMRT

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AAPM 2007

Adult prostate treatment

Pediatric CSI65

Same protocol Linac vs. Helical Tomo

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TomoTherapy

Some Concerned Issues

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Longer Treatment Time!!

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Future of TomoTherapy

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Prepare for Adaptive RT

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TomoDirectDiscrete -angle delivery mode

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Future Direction

Thank You for Your Attention!

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