Financial Disclosure
Helical Tomotherapy
I am a co-founder of TomoTherapy Inc.
(Madison, WI) which is participating in the
commercial development of helical tomotherapy.
Thomas Rockwell Mackie
Professor
Depts. Of Medical Physics, Human Oncology,
and Engineering Physics
University of Wisconsin
Madison WI 53706
Assembly Floor
trmackie@wisc.edu
TomoTherapy’s New Madison WI Facility
AAPM Summer School on IMRT, Colorado College, 2003
Additional Contributors
to this Talk
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Gustavo Olivera
Jeff Kapatoes
Ken Ruchala
Paul Reckwerdt
John Balog
Richard Schmidt
Dave Pearson
Eric Schloesser
Ray MacDonald
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Robert Jeraj
Minesh Mehta
Mark Ritter
Jack Fowler
Harry Keller
Weiguo Lu
Jeni Smilowitz
Wolfgang Tomé
Rufus Scrimger
Lisa Forrest
HI-ART Tomotherapy Unit
Gun Board
www.tomotherapy.com
UW Helical Tomotherapy Unit
Status June 2003
•FDA 510(k) cleared.
•Lung tumor and prostate verification CT scans obtained.
•Featured in NIH Program Project grant.
•In clinical use.
•To be replaced by HI-ART unit during fall 2003.
Geometry
6 MV X-Ray Source
(850 Gy/min, 1.5 mm point source)
Linac
Primary Collimator
Control
Computer
(0 to 5.0 cm Slice Width)
Binary MLC
Circulator
(64 leaves, ea @ 0.6cm)
85cm
Magnetron
Pulse Forming
Network and
Modulator
High Voltage
Power Supply Beam Stop Detector
85 cm Gantry Aperture
40 cm CT FOV
Approximately
50cm
Data Acquisition System
CT Detector System
1
Helical Delivery
Slice Width
Pitch = Distance Traveled Per Rotation
Slice Width
Modulated Helical Delivery into
Scintillation Fluid
Modulated Helical Delivery into
Scintillation Fluid
Modulated Helical Delivery into
Scintillation Fluid
Adaptive Radiotherapy
3-D Imaging
Deformable
Dose
Registration
Optimized
Planning
Verification CT
+ Image Fusion
Dose
Reconstruction
Treatment
With Delivery
Verification
Modify
Setup
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Prostate Case
Dose Rate
Beam on Time
2 min
Prostate Case
Cumulative Dose
CTV
PTV
Rectum
Bladder
0 to 30% 30 to 90% 90 to 100%
PTV= Pr + 4mm
PTV= (Pr+SV) + 4mm
L&R FH
Bladder
Rectum
Rectum
L&R FH
Bladder
Nasopharyngeal Tomotherapy Movie
Dose Rate
Cumulative Dose
CTV54 Gy
R.Parotid
GTV
CTV66 Gy
CTV60 Gy
Spine
L.Parotid
0 to 30% 30 to 90% 90 to 100%
3
Head & Neck Case
Limited Field
Prone Breast
Beam on Time
9 min for 2.2 Gy/fx
PTV 2
PTV 1
Lt.
Parotid
Cord
Rt.
Parotid
Limited Field
Prone Breast
Lumbar Irradiation
Skin
GTV
PTV
Kidneys
Muscle
PTV
Lt Lung Rt Lung
Lumbar Irradiation – Dose Comparison
CT Image Guidance
3
Dose (Gy)
Verify & Register CT (VRCT)
2.5
2
Series1
1.5
Ion Chamber
Series2
Calculation
• CT is fully volumetric.
• Able to image all treatment sites (breast, prostate,
H/N, etc.).
• MVCT pixel values have physical meaning and value.
• No high-Z artifacts (hip prostheses, fillings, etc.).
• Fully integrated with treatment unit console.
Series3
1
Series4
0.5
0
-40
-30
-20
-10
0
-0.5
10
20
30
40
Vertical (Z) (cm)
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Verification CT of a RMI CT Phantom at 3 cGy
Verification CT of a Lung Cancer Patient at 3 cGy
Soft Tissue Window
Lung Window
-3%
0%
-60%
6%
Lung
Tumor
Airholes: 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2 mm diameter. Contrasts: 0%, -60%, -3%, 6%.
Hip Prosthesis
Verification CT
Planning CT
Automatic Registration
Dental Fillings
Verification CT
Planning CT
Demonstrating Setup Modification
Using the Rando Phantom
Reference CT Image to Verification CT image
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Rando Phantom Setup 10 mm Off
in Longitudinal Direction
Position Corrected Automatically
Registration Results
Obese Patient
Verification CT with integrated registration and repositioning identified
offsets of -31.5 mm lat., 39.2 mm long., and 8.3 mm vert.
Patient Registration-Transverse
Patient Registration-Coronal
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Daily Variation in Laser-Based Setup
Tools for Patient Registration
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Grayscale – Planning CT
Green - VRCT
Position (mm)
10
Sagittal
5
0
-5
1
2
3
4
5
6
7
8
9
Lateral
Longitudinal
Vertical
-10
Standard Dev.
Lateral=3 mm
Long.=9 mm
Vertical=6 mm
-15
-20
-25
Day
Axial
Lumbar Spine Patient
Tools for Patient Registration
Perception Vs. Reality
Perception
Registration to VRCT Using Planned Isodoses
Contours
Grayscale – Planning CT
Bluescale – VRCT
Electron Beams Needed?
Reality
Electron Beams
Cannot do without
them.
Tomo dose
distributions are
usually better.
Non-Coplanar
Fields
Delivery
Efficiency
Unwanted Dose
They are difficult to
use, but useful.
Tomo throughput is
low.
Leakage and dose
outside the field are
greater.
They are rarely
needed for IMRT.
Tomo has highest
IMRT throughput.
Unwanted dose is
lowest for
tomotherapy.
Range of
Applicability
Tomotherapy is a
boutique system.
Tomo expands the
capability of IMRT.
Non-Coplanar Fields Needed?
Comparison of 16 MeV Electron Field
and TomoTherapy HI-ART System
HI-ART
16 MeV
Beam on Time
is 30 min for
6 mm Slice Width
and 13 Gy.
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Non-Coplanar Fields Needed?
Non-Coplanar Fields Needed?
L. Parietal
Tumor
L. Frontal
L. Optic Nerve
L. Occipital
Normal
Brain
Skull Irradiation
Non-Coplanar Fields Needed?
Delivery Efficiency
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Rt Optic Nerve
PTV
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Rt Eye
Lt Eye
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Chiasm
Helical tomotherapy is more efficient than other forms
of MLC-based IMRT.
Dose rates are higher than conventional radiotherapy.
Pitch = Distance Traveled Per Rotation/Slice Width.
Pitches from 0.2 to 0.5 are typically used for single
helix delivery.
Helical pitch is less than 1 which means that multiple
rotations pass over each point; in other words, the
slices overlap.
Overlap allows a larger slice width to be used and still
maintain reasonable resolution.
Slice widths of 2.5 cm and 5 cm are typically used.
Unwanted Dose?
Dose Profile
Unwanted Dose?
Reasons for Less Unwanted Dose
Linac
5 cm Jaw Width
1.5 cm Depth
Up to 23 cm of Tungsten
In the Primary Collimator.
Primary
Collimator
MLC
jaw motion
Leaves are 10 cm of Tungsten.
s
i n
g
l e
Z
Very Low
Dose Outside
Field
jaw motion
Y
M
L
C
l e
a
f
other leaves are into
and out of page
No Field Flattening Filter to
Cause Scatter Outside the Field.
Less Head Scatter from
Narrow Fields.
Detector
Beam Stop
10 cm Thick Lead Beam Stop
Behind the Radiation Detector.
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Conformal Mantle Field
Range of
Applicability?
TBI (Total Bone Irradiation)
Range of
Applicability?
Beam on Time
is 19 min for
5 cm Slice Width
and 1.2 Gy/fx!
Courtesy
Tim Schultheiss, Ph.D.
City of Hope
Conclusions
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Questions?
Helical tomotherapy is in clinical practice.
PTV dose is very homogeneous.
Normal tissue irradiation can be well avoided.
Bone and many soft tissue structures are visible with
tomotherapy verification CT.
No metal artifacts with tomotherapy verification CT.
No need for invasive immobilization or fiducial markers for
radiosurgery.
Setup verification based on CT image fusion.
Adjust setup using couch and laser movement.
Helical tomotherapy delivery is efficient.
Less unwanted dose.
Helical tomotherapy increases the capability of IMRT.
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