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UC SF
IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
MV Cone Beam CT
Jean Pouliot, Ph.D.
Professor
UCSF Comprehensive Cancer Center
San Francisco

IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
Objectives:
• Basic principles of MV CBCT
• Workflow of IGRT with MV CBCT
• Range of applications of MV CBCT
– Patient positioning
– monitoring of anatomical changes, tumor tracking
– planning purposes and in-situ dose calculation
– Tomosynthesis
• Future possibilities of MV CBCT for Dose-Guided
Radiation Therapy (DGRT).

UCSF
• Michelle Aubin
• Jean-Francois Aubry
• Kara Bucci
• Albert Chan
• Josephine Chen
• Hong Chen
• Cynthia Chuang
• Martina Descovitcz
• Bruce Faddegon
• Amy Gillis
• Olivier Morin
• Mack Roach III
• Joycelyn Speight
• Lynn Verhey
• Ping Xia
Main Collaborators
Siemens
• Ali Bani-Hashemi
• Fahard Ghelmansarai
• Paco Hernandez
• Dimitre Histrov
• Bijumon Gangadharan
• Matthias Mitschke
This work is supported
by
Siemens O.C.S.

Basic Principles of MV CBCT
Fan beam CT Cone-beam CT
1 slice per rotation Entire volume in 1 rotation

Basic Principles of MV CBCT
• MV CBCT generates a 3D
image of the patient anatomy
from the same x-ray beam
(6MV) used for treatment.
• Image and x-ray beam share
the same isocenter.
• Patient 3D anatomy in
treatment position, moments
before dose delivery.

MV CBCT: Main Features
• Very low dose-rate linac beam (0.005 M.U. per degree)
• Beam Pulse Triggered Acquisition Mode
(Synchronized pulse-panel readout)
• High sensitivity a-Si Panel EPID (Optimized for MV)
• Integrated workstation: EPID deployment, image
acquisition, reconstruction, fusion with CT, patient
alignment, treatment delivery

Basic Characteristics
of MV CBCT
• Half rotation: 200 degrees
• Acquisition ~ 45 seconds
• Acquisition + Reconstruction < 2 min.
• 27 cm x 27 cm x 27 cm Field of View
• Volume of 256 x 256 x 270
• Pixel size (0.5 mm)3
• Typical dose: 2 to 8 cGy
• Accurate Electron Density

MV CBCT

MV CBCT: Post processing
Diffusion filter reduces
noise and maintains edges

Future Beam Line for MV CBCT: LowZ tgt + No FF + 4.5 MV
Current BL Future BL Current BL Future BL
Courtesy of Bruce Faddegon, UCSF

Workflow of IGRT with MV CBCT
CT Dose Plan Patient alignment Dose Delivery
1: Image
Acquisition
2: Image
Reconstruction
S
!
o
r
F
X (voxel)
x (pixel)
3: Image
Registration
4: Patient
Alignment
X-offset
Y-offset
Z-offset

Workflow of IGRT with MV CBCT
• 1) The patient and the conebeam
acquisition mode are
selected at the treatment
console.
• 2) The linac gantry is placed
in starting position, namely
270 degrees.

Workflow of IGRT with MV CBCT
• 3) During the acquisition, the
gantry rotates 200 degrees until
it reaches its final position, 110
degrees.
During the rotation, a portal
image is acquired at each
degree. The reconstruction of
the cone-beam image starts
immediately after the first portal
image has been acquired.

Workflow of IGRT with MV CBCT
• 3) During the acquisition, the
gantry rotates 200 degrees until it
reaches its final position, 110
degrees.
During the rotation, a portal
image is acquired at each
degree. The reconstruction of the
cone-beam image starts
immediately after the first portal
image has been acquired.

Workflow of IGRT with MV CBCT
• 4) Upon completion of the
reconstruction image, the
cone-beam image is
automatically loaded in the
Adaptive Targeting
Sofware TM , and the CB to
CT image registration is
performed automatically in
few seconds using a mutual
information algorithm.

MV CBCT - CT Registration

Workflow of IGRT with MV CBCT
• 5) Proper alignment is
validated and manual
alignment can be performed
when fine-tuning is required.
• 6) The couch translation offset
values required to obtain
the best alignment of the
patient at isocenter are
displayed. The couch is
moved remotely from the
treatment console according
to these values and the
patient is ready for treatment.

Setup Methods
1. Conventional CT 2. Treatment Planning System
CT
2D method: DRR with EPI
DRR
3. Patient Setup
CT, Points & Contours
3D method: CT with MV CBCT

y = 1.00x + 0.00
R 2 = 0.99
Phantom Study
3 embedded gold seeds imaged at different locations:
MVCBCT Shift (cm)
Alignment of 3 Gold Seeds
2.00
1.50
1.00
0.50
0.00
-2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00
-0.50
IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
-1.00
-1.50
-2.00
EPI Shift (cm)

Dose Delivered
2 - 8 cGy @ isocenter
3-5 cGy : daily alignment
6-8 cGy : planning purpose

Dose Delivered

Compensation of dose delivered
Tx 96% * Tx + 40 daily 10 MU MV CBCT

Compensation of dose delivered
These DVHs demonstrate the possibility to nearly eliminate the
extra dose delivered to the patient for daily MV CBCT imaging.

Clinical applications of MV CBCT
• Patient positioning
• Head & Neck
• Lung
• Spine
• Chest
• Prostate
• Monitoring of anatomical changes
• Target delineation with non-compatible CT objects
• Dose calculation from MV CBCT to assess dosimetrical
impact (DGRT1)
• Dose-Guided Radiation Therapy (DGRT2)

Patient Setup and Prostate Alignment
3D Approach

IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
Daily Prostate Alignment
EPID + Markers

Prostate Alignment with MV CBCT
Reference CT MV CBCT 50% Blend CT-MV CBCT
Provides additional information over EPID+markers:
- Rectum, bladder, etc.
- Prostate contours

Patient Setup: Prostate Bed
Irradiation of postprostatectomy patient
Markers are
distinguished from
surgical clips for daily
alignment

The presence of a hip prosthesis often makes the
markers difficult to see on the lat EPI.
LAT
Patient Setup: Prostate
AP
MV CBCT could be used for marker detection and
prostate alignment with less dose than the regular
2D approach.
MV CBCT with only
1.8 M.U. (1.3 cGy)

Hip Prosthesis
In 2005 in US and Europe,
more than 500,000 people had a hip replaced.
IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
MV CBCT

Patient setup: Head & Neck
6 mm

Monitor Weight Loss

Day 1
Monitor Weight Loss
3D rendering of CT 3D rendering of MV CBCT
Day 23

Aligned with MV
CBCT
Lung
Aligned
according to EPI

Paraspinous Tumors
• Surgery + supporting hardware + post-op IMRT
• Spinal cord tolerance limits Dx (palliative)
• Image hardware artifact
– impairs target delineation
– hinders treatment verification
• MV CBCT -> Target definition
-> Daily 3D patient alignment
-> Improved confidence Dx (curative)

Treatment of Paraspinous Tumors
in the Presence of Orthopedic Hardware

Paraspinous Tumors: Patient Setup
Case Report
Mean magnitude of setup errors:
- Lateral: 3.6 mm
(95% C.I., 2.6-4.6 mm)
- Longitudinal: 4.1 mm
(95% C.I., 3.2-5.0 mm)
- Vertical: 1.0 mm
(95% C.I., 0.6-1.3 mm)

Paraspinous Tumors: Dosimetric Impact
4.1 mm
Dose
1.0 mm
3.6 mm
Without daily corrections:
(simulated in TPS)
Maximum dose (D 0.1cc ) to Spinal cord
would have increased from 51 to 61 Gy.
The CTV coverage decreased by 5 Gy.
Daily setup errors detected via MV CBCT were critical for both protection of
spinal cord tolerance and maintenance of CTV coverage.

Dose Calculation using MV CBCT

Dose Calculation using MV Cone-Beam CT

Dosimetrical Impact of Weight Loss
Week 1
IMAGE GUIDED ADAPTIVE
RADIOTHERAPY (IGART):
New Tools and
New Directions
Week 3
Differences in dose
distribution due to
anatomical changes
Δ(%) >5%
>10%

Dose-Guided Radiation Therapy
(DGRT)
DGRT is an extension of adaptive radiation therapy where
dosimetric considerations constitute the basis of
treatment modification
• Improved confidence that the dose is delivered as
planned
• Allow more aggressive and definitve treatment
(dose escalation)
• Better understanding of the outcome of treatments

Dose Plan
In-vivo
Dosimetry
Dose-Guided Radiation Therapy
In-situ
Dose
Calculation
(DGRT1)
In-situ
Exit
Dosimetry
In-situ
Dose
Reconstruction
(DGRT2)

MV CBCT: Summary
• Provide 3D anatomy of patient in treatment position
-> Patient Setup, Monitoring of anatomical changes
• Accurate electron density for dose calculation
-> Assess dosimetric Impact
• Facilitate dose reconstruction for DGRT
• Specialized imaging beam line and MV adapted Flat
panel EPID will further improve image quality

• MV Cone-Beam CT:
Thank You
– Pouliot et al., IJROBP, 61(2); 238-246, 2005
– Morin et al., Med. Dosi., 31(1);51-61, 2006
– Pouliot et al., Cancer et Radiothérapie, June 2006
• Exit Dosimetry with EPID:
– Chen et al., Med. Phys., 33(3); 584-594, 2006
• Dose Calculation with MV CBCT:
– Morin et al., submitted to IJROBP, 2006
• DGRT with MV CBCT:
– Chen et al., Brit. J. Radiol, June 2006
• Use of MV CBCT to complement CT for target definition in pelvic radiotherapy
in the presence of hip replacement:
– Aubin et al., submitted to Brit. J. Radiol., 2006
• IGRT using MV CBCT for Treatment of Paraspinous Tumors
in the Presence of Orthopedic Hardware
– Hansen et al., submitted to IJROBP, 2006