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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
AAPM 2003 Summer School - COS
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.
AAPM 2003 Summer School - COS
• 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
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
Recognizing the Broad Role of Physicists in Radiation Therapy
TG-40, Kutcher et al. (1994)
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AAPM 2003 Summer School - COS
How many institutions have quantitative support for their
CTV to PTV margin?
AAPM 2003 Summer School - COS
How many institutions plan to perform quantitative studies to estimate appropriate margins as
part of their IMRT implementation?
AAPM 2003 Summer School - COS
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.
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
• 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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AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
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)
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
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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AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
Cyberknife - Accuray Inc.Image-guided Radiosurgery
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
Introduction to Helical Tomotherapy
G. Olivera et al. – Tomotherapy, Middleton, WI
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AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
Automatic and/or manual registration and fusion
AAPM 2003 Summer School - COS
Automatic and/or manual registration and fusion
AAPM 2003 Summer School - COS
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)
AAPM 2003 Summer School - COS
(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
AAPM 2003 Summer School - COS
Filtered Back-Projection
Log & Weight
1D FFT-based Hamming
Filter4x 2D
Interpolation
Geometry
# of voxels # of projectionsRepeat ×
Reconstruction Volume
Feldkamp et al. (1984)
Σ
AAPM 2003 Summer School - COS
• 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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AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
Cone-beam CT of Head and Neck
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)
Cone-beam CT of Head and Neck
Axial512 x 512 matrix
0.5 mm pitch0.5 mm slice thickness
Dsurface = ~3 cGy
AAPM 2003 Summer School - COS
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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AAPM 2003 Summer School - COS
On-Board Imaging Concept
• Modes of operation• Radiographic• Cone Beam CT• Fluoroscopic•
On-Board Imaging ConceptASTRO 2002
Interfraction
Intrafraction
}
Works-In-Progress
AAPM 2003 Summer School - COS
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
AAPM 2003 Summer School - COS
CsI Screen – 3600 mg/cm2
0.388 mm
8-9 mm0.388 mm
Clinical Applications
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