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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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Siriraj Radiation Oncolgy
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 …….
Siriraj Radiation Oncolgy
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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Siriraj Radiation Oncolgy
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
Siriraj Radiation Oncolgy
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%
Siriraj Radiation Oncolgy
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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
Siriraj Radiation Oncolgy
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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Siriraj Radiation Oncolgy
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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Siriraj Radiation Oncolgy
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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Siriraj Radiation Oncolgy
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Dosimetric Advantage from Tomo but Integral Dose
increase 6.5 %
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Siriraj Radiation Oncolgy
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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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Siriraj Radiation Oncolgy
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TomoTherapy
Some Concerned Issues
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Longer Treatment Time!!
Siriraj Radiation Oncolgy
Future of TomoTherapy
7374
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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