Fundamental to Advanced Radiotherapy Treatment Technique
Transcript of Fundamental to Advanced Radiotherapy Treatment Technique
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Fundamental to Advanced
Radiotherapy Treatment Techniques (Imaging Session)
Sonjarod Oonsiri
King Chulalongkorn Memorial Hospital
Acknowledgement
• IAEA/RTC on Radiotherapy Techniques with Emphasis on
Imaging and Treatment Planning, Beijing, China (2012)
• Jake Van Dyk
• Howard Amols
• Paul Keall
Content
• Image for treatment planning system
• Image for target verification
Aim
• To provide overview of imaging techniques and dose
reporting concepts as defined by ICRU
Evolution of modern radiation therapy technology Tools for tissue delineation
• Simulator/Simulator-CT
• CT-simulator
• MRI-simulator
• Virtual simulation
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Simulator
• Advantage
▫ Reproduces treatment geometry
▫ Real-time breathing motion on fluoroscopy
• Limitation
▫ Limited external contour and
internal structure information
▫ No tissue density information
▫ Not useful for dose calculation
Simulator-CT
• Simulator with CT scanning mode
• CT option added ▫ Use image intensifier or flat panel detector
• Provide ▫ Internal/external contours
▫ Possibly tissue density information
▫ Poor image quality ; Inaccurate definition of target volume
http://www.varian.com
CT-simulator
• High resolution : Diagnostic images
• 3D reconstruction capabilities
(tumor/normal tissue localization)
• CT number/Electron density data
• High accuracy and precision of CT
number
Advantage of CT
• Widely available
• Good geometric accuracy
• Visualization of bony anatomy for comparison with radiograph
• Potential for rapid scanning
• With contrast, many tumors and nodes visualized reasonably well
4D-CT
• Tumour and organs can move up to 3
cm with respiration
• 4D-CT has applications in motion
inclusive, gated and tumour tracking
treatments
Keall et al, Aust Phys Engs Sci Med, 2002 Keall et al, Med Phys, 2006
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CT-simulation QA
• AAPM Report No.39 (1993) ▫ Specification and Acceptance Testing of
Computed Tomography Scanners
• AAPM Task Group No.66 (2003) ▫ Quality Assurance for Computed
Tomography Simulators and the Computed Tomography Simulation Process
• IAEA Human Health Series No.19 (2012) ▫ Quality Assurance Programme for
Computed Tomography : Diagnostic and Therapy Applications
Limitation of CT
Brain stem? Lesion?
Brain tumor King Chulalongkorn Memorial Hospital, Bangkok, Thailand
MRI-simulator
• Provide superior image quality for
soft-tissue delineation over CT
• Use careful patient positioning and
marking
• Determine the geometric
consistency between the CT and
MRI data sets
Fraass et al, IJROBP, 1987
Chen L et al, IJROBP, 2004
Eilertsen K et al, Acta Oncologica, 2008
Jonsson JH et al, Radiation Oncology, 2010
Accessory for MRI simulator
GE MRI Oncology Package http://www.lap-laser.com
MRI for TPS
• Advantage
▫ Better soft tissue contrast : Better definition of target and
critical structures
▫ Potential for functional MRI imaging can be used to localize
cancer
• Disadvantage
▫ Distortion
▫ Poor definition of bones
▫ Loss of electron density information
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MRI dose calculation
Chen L, IJROBP, 2004 Jonsson JH, Radiation Oncology, 2010
• The mass densities and electron density recommended in ICRU 46 (1992)
• The absolute dose agreement for PTV was within 2% between CT-based and MR-based
MRI in brachytherapy
• MRI is superior to CT for the
discrimination of GTV and
adjacent normal tissue
• In practice delineation seems
to be more accurate when using MRI
Potter R et al, Radiotherapy and Oncology, 2006
PET-CT
• Combines PET and CT in single gantry
system
▫ PET : Metabolic and functional imaging
▫ CT : Anatomic imaging
• PET-CT combination adds accuracy in
detecting and classifying tumors
• PET-CT planning changes cancer
patient management
▫ Target volume definition
▫ Tumor staging
Consistency ….
• How do we make sure that radiation oncology
professionals use consistent procedures and
terminology?
1978 1993
1999
Change over time
Purdy et al, Sem Rad Oncol, 2004
1978 1993 1999
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ICRU 83 ; 2010
• Irradiation techniques have advanced
▫ 3D-CRT to IMRT
▫ More availability of CT
▫ Additional imaging : MRI, PET, functional imaging
▫ Improved conformity
▫ More detailed dose-volume information on TPS
▫ Use of dose-volume constraints
▫ Automated optimization, IMRT
ICRU Report 83, 2010
ICRU 83 ; Dose reporting adapted to IMRT
• Dose accuracy ±5%
• Use of DVH
• No Dmin or Dmax instead …
• D98% and D2%
• Dose homogeneity and conformity
ICRU Report 83, 2010
Image for target verification
Image for target verification
• Ionizing radiation ▫ 2D imaging
Radiographic film
EPID
OBI/XVI
ExacTrac
Orthogonal kilovoltage localization
▫ 3D imaging
CT on rail
CBCT (KVCT/MVCT)
Image-Guided and Adaptive Radiation Therapy, 2010
• Non-ionizing radiation ▫ Ultrasound
▫ Electromagnetic (Calypso)
▫ Surface alignment (visionrt)
Portal radiograph
• The primary purpose of port filming is to
verify the treatment volume under actual
condition of treatment
• Film image is poor quality especially for
photon energies greater than 6MV
• Viewing is delayed because of the time
required for processing
AAPM Task Group 28, 1987
EPID
• Mount on the linear accelerator
• Daily imaging for treatment localization and verification may become feasible
• Acquisition, analysis, storage and distribution of portal images can be performed with relative ease
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CT on rail
Kuriyama K et al, IJROBP, 2003
Ma CM et al, Medical Dosimetry, 2006
On-board imager system
kV Imaging
King Chulalongkorn Memorial Hospital, Bangkok, Thailand
Cone beam CT 4D-CBCT
Sonke et al, Med Phys, 2005
CT CBCT 4D-CBCT
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ExacTrac
http://www.novalis-radiosurgery.com http://www.visionrt.com
Ultrasound
http://www.elekta.com
Real time tracking of target motion
http://www.calypsomedical.com
MRI guided external beam radiotherapy
Viewray Utrecht University
Alberta University Australian MRI-Linac Program
In-room MRI
• Integrated mobile MRI scanner (IMRIS) with linear accelerator
(TrueBEAM)
▫ Princess Margaret Hospital (Canada)
http://www.variantruebeam.com http://www.imris.com
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IGRT QA Recommendation
• AAPM Task Group No.75 (2007)
▫ The Management of Imaging Dose during
Image-Guided Radiotherapy
• Jean-Pierre Bissonnette et al (2008)
▫ A Quality Assurance Program for Image
Quality of CBCT Guidance in Radiation
therapy
• AAPM Task Group 142 Report (2009)
▫ Quality Assurance of Medical Accelerators
Future trend
• Knowledge based segmentation
▫ Automatic contouring based on pre-
contoured from database created by renowned radiation oncologist
▫ Reduce structure segmentation time
from hours to minutes
• Deformable registration
▫ Algorithm employs millions of degree of
freedom for the registration
▫ More accuracy for image registration
http://www.varian.com
http://www.mimsoftware.com
Summary
• Appropriate imaging is crucial for accurate target volume and
normal tissue delineation
• In treatment room imaging is important for reducing margins
• ICRU reports help to provide …
▫ Consistency in target volume definition
▫ Consistency in dose prescription
▫ Consistency in reporting
Tumor dose
Normal tissue dose