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Jean Pouliot, Ph.D.
Professor
Helen Diller Family UCSF Comprehensive Cancer Center,
AAPM CE-Therapy Series (SAM), July 29th, 2008
1
Disclaimer
Part of the work performed
on MVCBCT at UCSF
is supported by Siemens OCS.
2
Course Objectives
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J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
3
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J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
4
Why MVCBCT for pelvic patients ?
Faster, objective and less dose than EPID + markers
- 3-4 minutes
- 3 cGy
Provides additional 3D information
- Volumetric info: Rectum, bladder, etc.
- Prostate contours -> Dose recalculation
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
5
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
6
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Imaging in presence of Hip Prostheses
- Target delineation
- electron density
- marker visualization
Prostatectomy patients
- Surgical clips vs markers
HDR Brachytherapy
- Target delineation
- Non-compatible CT applicators
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
7
Spinal cord delineation with MVCBCT registered to CT for planning purpose,
for a patient with a metallic supporting structure
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
8
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J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
9
Concurrent treatment of prostate and pelvic lymph nodes with IMRT
Challenge: Independent movements of prostate vs nodes
Courtesy of Ping Xia, UCSF 2007
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
10
ADAPTIVE STRATEGY using Daily MVCBCT
for Pelvic Nodal Irradiation in the Treatment of Prostate Cancer
1- CT-MVCBCT registered on bony structures:
-> patient aligned accordingly: setup error
2- CT-MVCBCT registered on gold markers
-> prostate shift is the difference between
these two alignments
3- Select and treat with a (pre-calculated) plan
according to relative prostate shift
- Set of pre plans with iso shifts (iso)
- Shifting selected MLC leaves (mlc)
- Re-optimization of the plan (reopt)
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
11
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D&2*3(#/%5973(.#%0#E9#F3G3)1#H2A2)2*J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
12
MVCB Digital Tomosynthesis
MVCBDT is a limited arc MVCBCT (20o-40o vs. 200o)
Portal imaging
MVCBDT
2D
low contrast
fast acquisition
(few seconds)
1-3 MU
Some 3D
Better contrast than
EPID
faster acquisition and
lower dose than CB
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
MVCBCT
True 3D
longer acquisition
(~1 minute)
2-10 MU
Courtesy of M.Descovich, UCSF
13
MVCB Digital Tomosynthesis
Limited reconstruction arc results in tomographic noise, which increases as the arc decreases:
•
Out of focus structures are reconstructed on the plane of interest ! slice thickness
•
Shape distortion
•
Image artifact from different densities materials
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
Courtesy of M.Descovich, UCSF
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Clinical Images
EPID
DTS 40o
MVCBCT
EPID: only 2D
information,
poor contrast
DTS: spatial blur,
better contrast
CBCT: thin slices,
improved contrast
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
15
MVCB DT: Conclusions
• Image quality in DT depends on the reconstruction arc
• MVCB DT image quality is sufficient to provide anatomical information
and might be suitable for registration purposes.
• Advantages:
- Only a portion of the patient body gets exposed
- Faster
- Smaller dose
• Possible clinical application: lung patients
- Reduce the motion blur in imaging moving targets
- Acquire images during breath-holding
- Online verification of 4D and respiratory gating techniques
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
16
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J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
17
Optimizing Image Quality:
New Imaging Beam Line (IBL)
Remove flattening Filter
- non-uniform illumination
- smaller focal spot size
- Do not filter out low-E photons
Use Carbon Target
- Generate more low-E photons
Reduce Beam E to 4 MeV
- Generate more low-E photons
Courtesy of B. Faddegon, UCSF-2007
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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Requirements for Dose Recalculation
Stability of CT Number
Time
Target location
Patient size
Imaging dose
Complete Anatomy
Longitudinal + lateral directions
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
19
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Is the initial plan still valid?
When to replan?
What is the dosimetrical impact?
DGRT is based on the Availability of the 3D Dose Distribution “of the Day”
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
20
Accurate Dose Calculation can be obtained with MVCBCT
Morin et al., IJROB. 67(4),1202-1210; 2007.
CT
MVCBCT
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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Dosimetric impact and when to replan ?
Dose difference
Week 1
Week 1
Week 3
Week 3
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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Clinical studies
H&N: Variation from planning dosimetric endpoints
of the parotid glands and spinal cord.
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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Availability of the
Dose Distribution “of the Day”
Assess the dosimetrical impact
e.g. Patient setup, Anatomical change, Tumor shrinkage,
Weight loss, etc.
Global quality assurance “in-vivo”
e.g. Treatment documentation
More Precise (Delivered-)Dose Response vs
Outcomes
Enables Dose-Guided Radiation Therapy
DGRT is an extension of ART where dosimetric
considerations constitute the basis of treatment
modification and validation.
J. Pouliot
AAPM CE-Therapy Series (SAM), July 29th, 2008
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