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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