X-ray Guided IMRT
Contributors
Fang-Fang Yin – Henry Ford Hospital, Detroit, MI
David A. Jaffray, Ph.D.
G. Olivera – Tomotherapy, Middleton, WI
J. Pouliot – UCSF, San Francisco, CA
Radiation Physics Department
Radiation Medicine Program
Princess Margaret Hospital
University Health Network
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
MGH
Varian
Lecture,
2003
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
– 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
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 dosimetric
precision 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.
AAPM 2003 Summer School - COS
Recognizing the Broad Role of
Physicists in Radiation Therapy
IMRT System Components
• Prescription Method
• Structure Definition (target and normal)
• Setup Aids & Immobilization Devices
Herring DF, Compton DMJ: “The degree of
precision required in the radiation dose delivered in
cancer radiotherapy”
Brit J Radiol 5:1112-1118, 1970
Residual
Geometric
Uncertainty
PTV
Margins
TG-40, Kutcher et al. (1994)
AAPM 2003 Summer School - COS
1
How many institutions plan to
perform quantitative studies to
estimate appropriate margins as
part of their IMRT
implementation?
How many institutions have
quantitative support for their
CTV to PTV margin?
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
AAPM 2003 Summer School - COS
QA Tools of the Trade
Dosimetry
Mechanicals
–
–
–
–
–
–
– Levels
– Mechanical
“Gizmos”
– Service/Support
– Film
– QA Phantoms
– Record Keeping
Tools
Chambers
Electrometers
Film/Scanners
Diodes/Arrays
Calib. Services
Record Keeping
Tools
Geometric
Delivery
Precision
–
–
–
–
–
–
–
Portal Films
EPIDs
CT-Sims
Analysis Tools ?
Decision Tools ?
Margin Tools ?
Databases ?
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 patientspecific planning target volume in adaptive
treatment process for prostate cancer. (Yan et al.)
• Int J Radiat Oncol Biol Phys. 2000 Aug 1;48(1):
AAPM 2003 Summer School - COS
AAPM 2003 Summer School - COS
2
Margin Calculator
T. Craig, Ph.D.
Uncertainty distributions
Target volume
Dose distribution
Dose goal
Imports
RTOG
Format
Confidence limit
Simulation type
Employs
CERR2,
Deasy et al.
Slide 13
AAPM 2003 Summer School - COS
Bias
Line
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
Varian’s PortalVision aS500
Elekta - iView
GT
AAPM 2003 Summer School - COS
Bias Line
a-Si:H
FET
a-Si:H
Sensor
•
•
•
•
•
One Pixel
Data
Lines
a-Si:H
Schematic
Electronic Portal Imaging Systems
FET
Control
Lines
Data Line
Photodiode
Antonuk,et al
Med.Phys. 19:
1455-1466 (1992)
Contact
Pads
External Charge
Sensitive Pre-amp
aS500 Flat Panel
TFT Switch
Gate Line
Perkin-Elmer Prototype Panel
(20 cm x 20 cm)
Gate
Drivers
Signal
ASICs
Courtesy of Rolf Stähelin - Varian, Baden
18MV, 15 MU
3
Varian - 6 MU, 18 MV
Lateral Pelvis
18 MV 16 MU
AAPM 2003 Summer School - COS
Courtesy of Herman, M., Kruse, J. et al. - Mayo Clinic
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)
Courtesy Jon Kruse - Mayo
kV Portal Imaging on a 60Co Unit
“X-otron”
PMH/OCI
1958-1983
X-ray Tube Housed in the Head
AAPM 2003 Summer School - COS
AAPM 2003 Summer School - COS
kV Portal Imaging on a Clinac-18
H.E. Johns et al.(1959)
Room-based kV Localization
• Brain Lab Exac-trac – Henry Ford Hospital
• Cyberknife System – Stanford, Ca
• Shirato et al., Hokkaido University School
of Medicine, Japan.
Biggs et.al. IJROBP (1985)
AAPM 2003 Summer School - COS
4
BrainLAB ExacTrac/Novalis Image Guidance
System - Calibration
Image-Guided Extracranial Target Localization
•
•
•
X-Ray acquisition on treatment couch
Computerized generation of DRRs
Automatic comparison of live X-ray
images with DRRs
Ceiling
Mounted X-ray
Tubes
Calibration Phantom
Referenced to
Isocenter
Iso-center
reproducibility
based on the
imaging system
is within 1mm.
Pos. 1
FPI
20.5 x 20.5 cm2
Pos. 2
Live
X-Rays
DRRs
Yin et al., Henry Ford Hospital, Detroit, MI
AAPM 2003 Summer School - COS
Accuray - Cyberknife
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 ceilingmounted x-ray tubes.
4. Radiographic imaging
up to 2 times per
minute.
5. Fast automated DRRbased registration
algorithm (bone or
Localization precision: 1 s.d.: 0.7mm, 0.9o
markers).
AAPM 2003 Summer School - COS
AAPM 2003 Summer School - COS
Accuray - Cyberknife
Discrepancy =
“shift”
…
I
Tx
Tx
I
I
Tx
t
30-120 seconds
Range of Corrections by Anatomical Region
AAPM 2003 Summer School - COS
Cranial
Cervical Spine
Lung and
Pancreas
Thoracic and
Lumber Spine
Bony
Anatomy
Bony
Anatomy
Markers
(4 Au Markers
+ BH)
Markers
(4 Au
Markers)
0.85 mm
0.85 mm
1-3 mm
0.86 mm
Murphy et al. Int J Rad Oncol Biol Phys 55(5) 2003
Murphy et al. Int J Rad Oncol Biol Phys 55(5) 2003
Real-time
Tumor-tracking
System for
Gated
Radiotherapy
Highly Integrated System (4 xray tubes, 4 Image Intensifiers)
Temporal Resolution: 30 fps
Spatial Targeting Precision: 1.5
mm @ 40 mm/s
Shirato H et al., Hokkaido University School of Medicine, Sapporo, Japan.
5
Soft-tissue Imaging of Internal
Structures
• Guide therapy according to internal softtissue anatomy.
• Stronger correlation between imaged
contrasts and target anatomy.
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
Shirato H et al., Hokkaido University School of Medicine, Sapporo, Japan.
In-room
Conventional
CT for IGRT
• Computed Tomography (kV conventional,
MV “conventional”, cone-beam flat-panel kV
and MV)
AAPM 2003 Summer School - COS
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
Kuriyama et al. Int.J.Rad.Onc.Biol.Phys. 55(2) Feb 2003
CT Guidance
AAPM 2003 Summer School - COS
Onishi et al. Int.J.Rad.Onc.Biol.Phys. 56(1) May 2003
Introduction to Helical Tomotherapy
Portal-based
Verification
AAPM 2003 Summer School - COS
Onishi et al. Int.J.Rad.Onc.Biol.Phys. 56(1) May 2003
AAPM 2003 Summer School - COS
G. Olivera et al. – Tomotherapy, Middleton, WI
6
University of Wisconsin TomoTherapy
MVCT, 3 cGy
AAPM 2003 Summer School - COS
G. Olivera et al. – Tomotherapy, Middleton, WI
Automatic and/or manual registration and fusion
AAPM 2003 Summer School - COS
Cone-beam Computed Tomography for
Image Guidance in Radiation Therapy
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
Cone-Beam Computed Tomography
(a)
(b
• Kilovoltage
– Jaffray et al. - WBH/PMH
• Megavoltage
Robust 2D Detector
– Ford et al. – Memorial Sloan Kettering, NY, NY
– Hesse et al. – DKFZ, Heidelberg, Germany
– Pouliot et al. – UCSF (with Siemens)
Feasible Reconstruction Method
AAPM 2003 Summer School - COS
AAPM 2003 Summer School - COS
7
Bench-Top Cone-Beam CT System
Processing of Projection Data
X-ray Exposure
50 mA, 3 ms (0.15 mAs)
120 kVp
2 mm Al + 0.127 mm Cu
14.6° Cone Angle
Gain and
Offset
Detector Read-Out
Exposure
Normalization
Pixel Defect
Correction
1024 x 1024
3.5 frames/sec (max)
300 Projections
Object Rotation
1.2° per projection
Repeat for
300 Projs.
Filtered Back-Projection
Log &
Weight
Geometry
1D FFT-based
Hamming
Filter
Reconstruction
Volume
X-ray Image-Guided RT
4x 2D
Interpolation
Elekta Synergy “RP”
4 Units Worldwide
Σ
(Christie, WBH, PMH, NKI)
• Retractable kV X-ray
Imaging System
• Volumetric CT Imaging
Feldkamp et al. (1984)
AAPM 2003 Summer School - COS
Repeat ×
# of voxels
# of projections
• Calibration between
imaging and delivery
systems
X-ray Tube
Mounted at 90o
AAPM 2003 Summer School - COS
Cone-beam CT Set of Head Phantom
Product Release May 2003
Unit at William Beaumont Hospital
Royal Oak, MI
Transverse
Coronal
Sagittal
Accelerator-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
8
Cone-beam
CT of Human
Thigh
Cone-beam
CT of Human
Pelvis
Acquisition Parameters:
Coronal
512 x 512 matrix
0.5 mm pitch
0.5 mm slice thickness
Dcenter = ~0.5 cGy
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.
AAPM 2003
Summer School
- COSP.
Coronal
Williams and V. Khoo, Christie Hospital, Manchester, UK
Cone-beam
CT of Head
and Neck
Head
512 x 512 x 512 matrix
0.5 mm cubic voxels
Dsurface = ~3 cGy
AAPM 2003 Summer School - COS
Courtesy of Drs. P. Williams and V. Khoo, Christie Hospital, Manchester, UK
Neck and Lung
Cone-beam
CT of Head
and Neck
512 x 512 x 512 matrix
0.5 mm cubic voxels
Dsurface = ~3 cGy
Original Prototype, SL01 - WBH (IDE)
Cone-beam
CT of Head
and Neck
AAPM 2003 Summer School - COS
Original Prototype, SL01 - WBH (IDE)
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
Axial
512 x 512 matrix
0.5 mm pitch
0.5 mm slice thickness
Dsurface = ~3 cGy
AAPM 2003 Summer School - COS
• Dynamic range of FPIs
– Driven by fluoroscopy applications in medicine
• Breathing motion during acquisition
Original Prototype, SL01 - WBH (IDE)
AAPM 2003 Summer School - COS
9
Works-In-Progress
Works-In-Progress
On-Board Imaging Concept
•
•
•
•
•
Preliminary CT Results
Modes of operation
Radiographic
Interfraction
Cone Beam CT
Fluoroscopic
Intrafraction
}
• Images courtesy of Varian scientists and engineers
AAPM 2003 Summer School - COS
On-Board Imaging Concept
ASTRO 2002
MV Cone-beam CT with a FPI.
Flat Panel Detector
Hiemann RID 256-L
Flat-Panel
256 x 256, 800 um
Cu/Gd2O2S:Tb
1 frame/79 ms
12-bit ADC
Comparison of MV
FPI-CBCT
Performance
for MV and kV
a
X-rays
b
kV
kV: 100kVp, Elekta SL20
1.05 0.945
3 mm slice
Liver 1.05
PE
0.945
Water 1.00
Breast 0.98
Brain 1.039
Resin 1.02
Integer number of
x-ray pulses per
projection.
mg/cm2
26.7 cGy
61.3 cGy
MV: 6MV, Elekta SL20,
500-1900 projections
over 360o
CsI Screen – 3600
AAPM 2003 Summer School - COS
1.02
1.039
c
5.8 cGy
1.00
0.98
kV
~1.3 cGy
Groh et al. Med. Phys. 2000
Clinical Applications
0.388 mm
0.388 mm
8-9 mm
AAPM 2003 Summer School - COS
10