X-ray Guided IMRT Contributors · Dose: ~1 cGy Elekta Synergy Research Platform Courtesy of Drs. P. Williams and V. Khoo, Christie Hospital, Manchester, UK Acquisition Parameters:

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AAPM 2003 Summer School - COS

X-ray Guided IMRT

David A. Jaffray, Ph.D.

Radiation Physics DepartmentRadiation Medicine ProgramPrincess Margaret HospitalUniversity Health Network

MGH – Varian Lecture, 2003 AAPM 2003 Summer School - COS

ContributorsFang-Fang Yin – Henry Ford Hospital, Detroit, MI

G. Olivera – Tomotherapy, Middleton, WI

J. Pouliot – UCSF, San Francisco, CA

P. Munro – Varian Medical Systems, Palo Alto, CA

J. Wong – William Beaumont Hospital, Royal Oak, MI

T. Haycocks – Princess Margaret Hospital, Toronto, CA

T. Craig – Princess Margaret Hospital, Toronto, CA

M. Herman – Mayo Clinic


Implementation of Intensity Modulated Radiation Therapy

• A lot of ‘old baggage’ that seems to need resorting.• Arising from:

– A new found capacity to generate and place dose gradients.– A desire to avoid normal structures for complication

reduction and/or dose escalation.• Putting significant pressure on the margins that we

have been using in conventional RT (both CTV and PTV/PRV).

• Heightening the need for an approach that can provide confidence in the PTV margin.


• Recommends that the dose delivered over the course of treatment be known to within ± 5%.

• Achieving this level of accuracy and precision requires that each step of the treatment process performs at a dosimetricprecision much better than 5%.

• This places stiff tolerances on both (i) the precision of the clinical dosimetry and (ii) the geometric precision in delivery and planning.

• To achieve and maintain the desired level of precision, it is recommended that a system of treatment delivery be constructed considering dosimetric and geometric factors.

Herring DF, Compton DMJ: “The degree of precision required in the radiation dose delivered in cancer radiotherapy”

Brit J Radiol 5:1112-1118, 1970


IMRT System Components• Prescription Method• Structure Definition (target and normal)• Setup Aids & Immobilization Devices

– Breast boards, masks, ABC• Positioning strategy

– Off-line and/or on-line evaluation and correction– Imaging or Other Data – Intervention

• Delivery Technique (gradients, delivery time, gating, tracking)

• Quality Assurance Checks

Residual Geometric

Uncertainty

PTV Margins


Recognizing the Broad Role of Physicists in Radiation Therapy

TG-40, Kutcher et al. (1994)

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How many institutions have quantitative support for their

CTV to PTV margin?


How many institutions plan to perform quantitative studies to estimate appropriate margins as

part of their IMRT implementation?


Patient and Process QA is Challenging

• Define the objectives up front.• Constrain the process.• Data-driven approach.• Need integrated tools to analyze the data• Requires a method of

maintaining/monitoring performance.


QA Tools of the Trade

– Chambers– Electrometers– Film/Scanners– Diodes/Arrays– Calib. Services– Record Keeping

Tools

Dosimetry– Levels– Mechanical

“Gizmos”– Service/Support– Film– QA Phantoms– Record Keeping

Tools

Mechanicals

– Portal Films– EPIDs– CT-Sims– Analysis Tools ?– Decision Tools ?– Margin Tools ?– Databases ?

Geometric Delivery Precision

AAPM 2003 Summer School - COS AAPM 2003 Summer School - COS

Margin Estimation Tools• Currently no commercial tools for this purpose.• Recommended reading:

– Inclusion of geometric uncertainties in treatment plan evaluation. (van Herk et al.)

• Int J Radiat Oncol Biol Phys. 2002 Apr 1;52(5):– An off-line strategy for constructing a patient-

specific planning target volume in adaptive treatment process for prostate cancer. (Yan et al.)

• Int J Radiat Oncol Biol Phys. 2000 Aug 1;48(1):

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AAPM 2003 Summer School - COS Slide 13

Uncertainty distributions

Target volume

Dose distribution

Dose goal

Confidence limit

Simulation type

T. Craig, Ph.D.

Margin Calculator

Employs CERR2,

Deasy et al.

ImportsRTOG Format


• Metal plate, Gd2O2S:Tb• 0.5-0.8 mm @ iso• ~25 cm FOV• multiple frames/sec• Synchronized readout to

reduce banding artifacts• Motorized support arm• Integrated acquisition and

analysis

Electronic Portal Imaging SystemsVarian’s PortalVision aS500

Elekta - iViewGT

a-Si:H Schematic FET

Control Lines

Data Lines

a-Si:H Sensor

a-Si:H FET

External Charge Sensitive Pre-amp

Contact Pads

Bias Line

Antonuk,et alMed.Phys. 19:

1455-1466 (1992)

One Pixel

Photodiode

Gate Line

TFT Switch

Bias Line

Data Line

aS500 Flat Panel

Courtesy of Rolf Stähelin - Varian, Baden

GateDrivers

Signal ASICs

Perkin-Elmer Prototype Panel (20 cm x 20 cm)

18MV, 15 MU

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Lateral Pelvis

18 MV 16 MU

Courtesy of Herman, M., Kruse, J. et al. - Mayo Clinic

Varian - 6 MU, 18 MV

Courtesy Jon Kruse - Mayo


kV Sources for Guidance a.k.a. ‘Back to the Future’

• A.F. Holloway, Brit.J.Radiol. 31: 227 (1958)• H.E. Johns et.al., Am.J.Roentgenol. 81: 4-12 (1959)• Weissbluth et.al., Radiology 72: 242-253 (1959)• L.M. Shevron et.al., Clin.Radiol. 17: 139-140 (1966)• H.P. Culbert et.al. IJROBP 10 Sup 2: 180 (1984)• P.J. Biggs et.al., IJROBP 11: 635-643 (1985)• R. Sephton et.al., Radiother.Oncol. 35:240-247 (1995)


kV Portal Imaging on a 60Co Unit

“X-otron”PMH/OCI

1958-1983

X-ray Tube Housed in the Head

H.E. Johns et al.(1959)

Biggs et.al. IJROBP (1985)

kV Portal Imaging on a Clinac-18


Room-based kV Localization

• Brain Lab Exac-trac – Henry Ford Hospital• Cyberknife System – Stanford, Ca• Shirato et al., Hokkaido University School

of Medicine, Japan.

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BrainLAB ExacTrac/Novalis Image Guidance System - Calibration

FPI20.5 x 20.5 cm2

Yin et al., Henry Ford Hospital, Detroit, MI

Ceiling Mounted X-ray

TubesCalibration Phantom Referenced to

Isocenter

Iso-center reproducibility based on the

imaging system is within 1mm.

Pos. 2Pos. 1

LiveX-Rays

DRRs

• X-Ray acquisition on treatment couch• Computerized generation of DRRs• Automatic comparison of live X-ray images with DRRs

Image-Guided Extracranial Target Localization


Cyberknife - Accuray Inc.Image-guided Radiosurgery


1. Ceiling mounted x-ray tubes.

2. X-band Accelerator on Robotic Positioning Unit.

3. Dual FPIs mounted opposite ceiling-mounted x-ray tubes.

4. Radiographic imaging up to 2 times per minute.

5. Fast automated DRR-based registration algorithm (bone or markers). Localization precision: 1 s.d.: 0.7mm, 0.9o

Murphy et al. Int J Rad Oncol Biol Phys 55(5) 2003

Accuray - Cyberknife


Range of Corrections by Anatomical Region

0.86 mm1-3 mm0.85 mm0.85 mm

Markers(4 Au

Markers)

Markers(4 Au Markers

+ BH)

Bony Anatomy

Bony Anatomy

Thoracic and Lumber Spine

Lung and Pancreas

Cervical SpineCranial

Murphy et al. Int J Rad Oncol Biol Phys 55(5) 2003

I Tx I Tx t

Discrepancy = “shift”

…

I Tx

Accuray - Cyberknife

30-120 seconds

Real-time Tumor-tracking

System for Gated

Radiotherapy

Shirato H et al., Hokkaido University School of Medicine, Sapporo, Japan.

Highly Integrated System (4 x-ray tubes, 4 Image Intensifiers)

Temporal Resolution: 30 fps

Spatial Targeting Precision: 1.5 mm @ 40 mm/s

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Shirato H et al., Hokkaido University School of Medicine, Sapporo, Japan.

Range of motion w.r.t. Tx port (4 patients with Ca Lung):

With real-time gating: 2.5-5.3 mm

Without real-time gating: 9.6-38.4 mm


Soft-tissue Imaging of Internal Structures

• Guide therapy according to internal soft-tissue anatomy.

• Stronger correlation between imaged contrasts and target anatomy.

• Computed Tomography (kV conventional, MV “conventional”, cone-beam flat-panel kV and MV)

AAPM 2003 Summer School - COSKuriyama et al. Int.J.Rad.Onc.Biol.Phys. 55(2) Feb 2003

In-room Conventional CT for IGRT

AAPM 2003 Summer School - COSOnishi et al. Int.J.Rad.Onc.Biol.Phys. 56(1) May 2003

In-room Conventional CT for IGRT

Positional Accuracy:

0.2 mm (LAT)

0.18 mm (VERT)

0.39 mm (LONG)

AAPM 2003 Summer School - COS Onishi et al. Int.J.Rad.Onc.Biol.Phys. 56(1) May 2003

Portal-based Verification

CT Guidance


Introduction to Helical Tomotherapy

G. Olivera et al. – Tomotherapy, Middleton, WI

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University of Wisconsin TomoTherapy MVCT, 3 cGy

G. Olivera et al. – Tomotherapy, Middleton, WI AAPM 2003 Summer School - COS

University of Wisconsin TomoTherapy MVCT, 2.5 cGy

G. Olivera et al. – Tomotherapy, Middleton, WI


Automatic and/or manual registration and fusion


Automatic and/or manual registration and fusion


Cone-beam Computed Tomography for Image Guidance in Radiation Therapy

• Kilovoltage– Jaffray et al. - WBH/PMH

• Megavoltage– Ford et al. – Memorial Sloan Kettering, NY, NY– Hesse et al. – DKFZ, Heidelberg, Germany– Pouliot et al. – UCSF (with Siemens)


(b(a)Cone-Beam Computed Tomography

Robust 2D Detector

Feasible Reconstruction Method

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Bench-Top Cone-Beam CT System

X-ray Exposure50 mA, 3 ms (0.15 mAs)120 kVp2 mm Al + 0.127 mm Cu14.6° Cone Angle

Detector Read-Out1024 x 1024

3.5 frames/sec (max)

Object Rotation1.2° per projection

Repeat for 300 Projs.

Processing of Projection Data

Gain and Offset

Exposure Normalization

Pixel Defect Correction

300 Projections


Filtered Back-Projection

Log & Weight

1D FFT-based Hamming

Filter4x 2D

Interpolation

Geometry

# of voxels # of projectionsRepeat ×

Reconstruction Volume

Feldkamp et al. (1984)

Σ


• Retractable kV X-ray Imaging System

• Volumetric CT Imaging

• Calibration betweenimaging and deliverysystems

X-ray Image-Guided RT

Elekta Synergy “RP”4 Units Worldwide

(Christie, WBH, PMH, NKI)

X-ray Tube Mounted at 90o

Transverse

Cone-beam CT Set of Head Phantom

CoronalSagittalAccelerator-based Acquisition; 320 Projections; 120 kVp, 200 mAs; 180 s.

(0.25 x 0.25 x 0.25) mm3 voxels AAPM 2003 Summer School - COS

Unit at William Beaumont Hospital

Royal Oak, MI

Product Release -May 2003

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Patient: 70 yr old female

FOV: ~25 cm in diameter

Reconstruction: 0.5 x 0.5 x 0.5 mm3

Tacq: 2 minutes (300 projections)

Dose: ~1 cGy

Elekta Synergy Research Platform

Courtesy of Drs. P. Williams and V. Khoo, Christie Hospital, Manchester, UK

Acquisition Parameters:

Coronal

Cone-beam CT of Human

Thigh

Cone-beam CT of Human

Pelvis

Coronal512 x 512 matrix

0.5 mm pitch0.5 mm slice thickness

Dcenter = ~0.5 cGy

Courtesy of Drs. P. Williams and V. Khoo, Christie Hospital, Manchester, UK


Cone-beam CT of Head and Neck

Head

Original Prototype, SL01 - WBH (IDE)

512 x 512 x 512 matrix0.5 mm cubic voxels

Dsurface = ~3 cGy



Neck and Lung

Original Prototype, SL01 - WBH (IDE)

512 x 512 x 512 matrix0.5 mm cubic voxels

Dsurface = ~3 cGy

AAPM 2003 Summer School - COS Original Prototype, SL01 - WBH (IDE)


Axial512 x 512 matrix

0.5 mm pitch0.5 mm slice thickness

Dsurface = ~3 cGy


Conebeam CT Issues• Detector field of view (~25 cm FOV, recon)

– Offset detector schemes• Elevated x-ray scatter

– Noise and Cupping Artifacts– Grids and algorithms

• Dynamic range of FPIs– Driven by fluoroscopy applications in medicine

• Breathing motion during acquisition

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On-Board Imaging Concept

• Modes of operation• Radiographic• Cone Beam CT• Fluoroscopic•

On-Board Imaging ConceptASTRO 2002

Interfraction

Intrafraction

}

Works-In-Progress


Works-In-Progress

Preliminary CT Results

• Images courtesy of Varian scientists and engineers

MV Cone-beam CT with a FPI.

Flat-PanelFlat Panel DetectorHiemann RID 256-L

256 x 256, 800 umCu/Gd2O2S:Tb1 frame/79 ms12-bit ADC

500-1900 projectionsover 360o

Integer number ofx-ray pulses per projection.

Comparison of FPI-CBCT

Performance for MV and kV

X-rays a b

c

61.3 cGy 26.7 cGy

5.8 cGy

MV

kV

MV: 6MV, Elekta SL20,

kV: 100kVp, Elekta SL20

3 mm slice

~1.3 cGy

kV

Liver 1.05PE 0.945Water 1.00Breast0.98Brain 1.039Resin 1.02

1.05 0.945

1.00

0.981.039

1.02

Groh et al. Med. Phys. 2000


CsI Screen – 3600 mg/cm2

0.388 mm

8-9 mm0.388 mm

Clinical Applications

Documents

X-ray Guided IMRT Contributors · Dose: ~1 cGy Elekta Synergy Research Platform Courtesy of Drs. P. Williams and V. Khoo, Christie Hospital, Manchester, UK Acquisition Parameters: