Prostate IGRT With Setup Intelligence 4sharing

Implementing an IGRT correction
strategy using IMPAC Setup
Assist/Intelligence
IMPAC Mid-Atlantic Regional Users Meeting
May 30, 2008
Carnell J Hampton, Ph.D.
Clinical Physics Section
Department of Radiation Oncology

W A K E F O R E S T U N I V E R S I T Y S C H O O L O F M E D I C I N E CJ Hampton
Learning Objectives
After completing this activity, the learner will be able
to:
Describe the elements of an IGRT on-line correction
strategy and discuss how members of the radiation
oncology team play a role in the successful
implementation of such a strategy
Understand and use tools available within MOSAIQ
to establish an IGRT correction strategy
Discuss challenges and potential pitfalls of the
WFUBMC experience implementing a clinical
implanted-marker prostate IGRT correction strategy
including quality assurance, chart documentation
and associated IGRT billing issues

Conformal Radiotherapy Planning
Goal: Optimize the
therapeutic ratio by
shaping delivery of
high-dose radiation
to the target volume
while sparing
surrounding normal
structures

Geometric Uncertainty/Errors
Knowledge of geometric uncertainties and their effect on accurate
RT are well documented
Patient specific geometric uncertainty has implications for
insufficient coverage of target or overdosage of normal tissues
Uncertainty can be classified into groups defined by the relative
relationship between the uncertainty and the patient and
treatment coordinate systems
Setup error
Separation/table sag
Voluntary movement during Tx
Respiration
Rectum/bladder filling
Peristalsis
Cardiac motion
Swallowing

Relative Uncertainty in RT
Advanced imaging, especially temporal imaging, has
aided the quantification of uncertainty for specific
disease sites.
Both simulations and clinical patient studies have
begun to document the extent to which geometric
uncertainty impacts therapy.
0-40 mm4-6 mmUp to 50 mmLung
3-4 mm3-4 mm3-4 mmProstate
6 mm4-6 mm6-42 mmBreast
Organ MotionSetupDelineationSite
Langen 2006

Geometric Uncertainties
ICRU 62 Terminology
CTV=>PTV
Includes:
IM – Internal
Margin variation in
shape and position of
CTV within patient
SM – Setup Margin
uncertainty in patient
position and beam
alignment
No explicit margin for target delineation, which is a function of inter-observer
variability and imaging modality
PTV
CTV
GTV
IM
SM

What is IGRT?
“Real-time” imaging consisting of:
1. 3D volumetrics of soft tissues
2. Efficient acquisition and comparison of the
3D volumetrics, and
3. An efficacious process for clinically
meaningful intervention
Ling et al, Radiotherapy and Oncology (2006)

IGRT is useful when:
conformality is critical,
dose escalation has been shown to provide a
benefit,
uncertainty due to tumor motion is a
concern,
changes in tumor or normal structures
during the course of therapy require
adaptation of the original treatment plan.
“IGRT is a quality assurance tool for
highly conformal treatment”

IGRT Process: On-line Correction
Initial Setup Analysis Action
TreatmentImaging Imaging
Modified from Yin et al, Med. Phys. Pub.
Imaging

Stereoscopic IGRT for On-line
Localization/Correction
Derived 3D localization through stereoscopic
imaging
Automated or semi-automated methods for
comparing reference/treatment-time images
Image registration or matching based on soft
tissue, bony anatomy, implanted markers (IM)
and clips, user-generated contours

Gold markers are
placed prior to CT
treatment simulation
A treatment plan
is created based
on the simulation
CT scan. The
tumor is
precisely
targeted for
radiation therapy.
Immobilization is created for each patient. A CT
scan is acquired for treatment planning and
measurements recorded for later setup.
A computer program is used to
calculate where the target is on
x-ray images and guides the
setup of the patient back to the
parameters of the treatment
plan.
Once the patient is in
the correct position,
radiation is delivered.
1.1.
2.2.
3.3.
4.4.
5.5.

IGRT Workflow: Therapists’/Dosimetrists’ Role
Pre-Therapy
Identification of matching
target (i.e. IM, contour) used
for on-line correction on
planning CT or MR
Daily Therapy
Performing patient setup,
image registration, and daily
on-line correction
Quality assurance monitoring
of image registration

IGRT Workflow: Physicians’ role
Patient selection for IGRT
Implantation of fiducial
markers
Review of image registration
results, daily imaging
Approval of daily images,
recommendations to improve
patient localization
Trend analysis of patients
translations over the course of
therapy

IGRT Workflow: Physicists’ Role
Acceptance testing and
commissioning of image
registration software
Determination of residual error
Investigating patterns of failure
Creating guidance documentation
Collaborating with M.D. to
determine shift action levels
Trend analysis of IGRT data
Clinical workflow analysis
Periodic QA

Why Prostate IGRT?
Known and unknownKnown and unknown knownsknowns
effect prostate RTeffect prostate RT
IGRT helps address someIGRT helps address some
knownknown knownsknowns
Elimination of systematic
errors in dose delivery to the
prostate will probably have a
positive impact on improving
the outcome of therapy
(Crevosier, IJROBP, 2005).
Conformal dose delivery toConformal dose delivery to
the target makes dosethe target makes dose
escalation feasibleescalation feasible
Wu et al, IJROBP, 2006

Prostate IGRT Comparison: Setup Accuracy
Figure 1
Comparison of
residual errors
for different
image-guided
correction
techniques in
prostate, in the
left-right (LR),
anteriorposteri
or, and
superior-
inferior
directions.
GS Mageras et al, Seminars in Rad. Onc., 2007
~2 mm

Implanted Marker IGRT (IM-IGRT):
Required Resources
Implantable Markers…
MV/kV Source & Digital Image Receptor
Localization Software
…& personnel
skilled at
implantation

MD
Workroom
/Office
IM-IGRT: Optional Resources
Treatment Console
Remote review tools
Trending/Data analysis tools

IM-IGRT
Direct or indirect imaging of the prostate alone with
human detection of setup errors is insufficient to
achieve high precision
Fiducial markers implanted via transrectal ultrasound
create a permanent implanted coordinate system.

IM-IGRT
3-5 markers typically implanted within prostate
Apex, mid-gland lateral, base
Markers can be localized with treatment beam (MV)
using orthogonal portal images or kV X-ray
source/detector
3 mm
0.8 mm

Implanted Marker (IM) IGRT
3D localization provided by the imaging of markers on orthogonal portal images and the
reconstruction of their position within the treatment coordinate system
Least-squares minimization technique used to reconstruct marker position in 3D
The reference frame defined by CT in treatment planning can be transformed in 3D to the
treatment coordinate system and registered with the location of the markers determined from
the orthogonal portal images
The registration gives the translations needed to align the isocenter determined from the
orthogonal images to the isocenter defined in treatment planning

Limitations of IM-IGRT (Known Unknowns)
IM-IGRT uses fiducials as surrogates for tumor
position
IM-IGRT methods generally account for
uncertainties resulting from interfraction rigid
organ motion and setup error
Margins needed to account for unaccounted for
uncertainties such as:
Deformation and rotation of the prostate caused by
intrafraction organ motion (eg. Rectal and bladder
filling, migration of intestinal gas)
Uncertainty in target/normal structure delineation

Sources of Uncertainty (Known Knowns)
Patient Localization (1-2mm)
Inaccuracies in the imaging and patient-
support systems
Marker Localization (1.5mm) 1
Finite marker size
Calculated fit of rigid body transformation
Image quality limitations
Marker Migration (1-2mm) 1,2
1Pouliot, IJROBP 2003
2Poggi, IJROBP 2003
PTV
CTV
GTV
IM
SM

Establishing Action Levels
Using purely geometric evaluations,
action levels can be established
considering the local planning margins
and estimates of the known
uncertainties.
An action level can be considered
reflecting the tradeoff between effort to
correct a patient’s position and the
desired precision level for treatment.

Establishing Action Levels
Planning margins* + uncertainty
Ex:
If the shift is <= 3mm, no couch move necessary
If the shift is >3mm but <=8mm, move couch as
directed. No verification image needed.
If the shift is > 8mm but <=15 mm, move couch as
directed. Acquire verification films. Repeat
localization as above.
If the shift is >15mm. Notify physics/physician.
* CTV-to-PTV = prostate + 7mm/5mm posterior; IMRT treatment planning

IM-IGRT using MOSAIQ
Setup Intelligence
Modules for image registration and fusion
Point registration
Curve registration
Manual registration
Method for implementing couch offsets for
on-line correction
Online and offline quantitative analysis tools
Support for third-party positioning software

Image Registration Definitions and “Rules”
2D image registration – registration of a
portal/verification image and reference
image (DRR) pair resulting in the
calculation of a 2D isocenter shift
Available only at cardinal angles (0, 90, 180,
270)
No verification images with couch rotations
The common dimension can be derived (i.e.
the sup/inf dimension for independent AP
and Lat image reconstruction)

R. Lat

AP

Image Registration Definitions and “Rules”
Stereoscopic image registration –
registration of 2 sets of
portal/verification image and reference
image (DRR) pairs resulting in the
calculation of a 3D isocenter shift
the image must be a portal image associated with the same site
the angle between incident beams must be greater than 30 and
less than 150 degrees to that of the review image
the study date and time must be within 10 minutes of the
review image
the image must be taken on the same treatment machine as the
review image
the image must have square pixels
the image cannot be approved, rejected, or voided.

Preparing for IM-IGRT Treatment
Departmental setup
Patient or Isocenter
Orientation
Site Setup
How to get there: from the
Diagnoses and Interventions
window, click Site Setup or
from the Treatment Field
Definition dialog box
Options menu, click Site
Setup.
Patient orientation must be
set

Registration Editor
Set isocenter, scale
Identify markers,
curves, landmarks for
future registration
Landmarks locked after
recording a registration

Point Registration
Image registration can be initiated from the treatment delivery table window.

Point Registration
Select the daily Images

Point Registration
Initiate image registration by clicking the Register button.

The other image of the stereoscopic pair is selected
and the image registration window opens.

#1
#2
#3
For each verification image, markers are identified
corresponding to the reference images

Graphically review the accuracy of the automatic image registration.

The calculated offsets are displayed in the image review window. Image
registration is complete!

Localization Trend Review

Offset References
Session (Localization) Offsets
Setup error data collected during the
treatment session
Third Party Offsets
Setup error data calculated using other
software can be manually added to a
patient’s treatment record
Prescribed Offsets
The systematic setup error can be
determined from session offsets

On-line Correction
Offset Couch Calculator
Calculates new couch targets relative to the
current couch location

Shifting the Patient
Setup Intelligence calculates and displays the new couch coordinates
based on the image registration offsets.

Initial Setup Imaging Analysis Action
TreatmentImaging Imaging
Modified from Yin et al, Med. Phys. Pub.

IM-IGRT: WFU Experience
WFUBMC IM-IGRT program initiated in 2006
50 patients treated with IM-IGRT (2006-
present)
Hardware/Software Configuration
4 Varian EX Linacs with EPIDs
ADAC Pinnacle TPS
PortalVision
ACCULOC markers/ISOLOC localization software
(2 licenses)
Multi-Access/MOSAIQ upgrade to Setup
Assist/Intelligence in April 2008.

Setup Intelligence: Advantages over Acculoc
Accessibility of image registration to multiple
linacs without the need for multiple software
licenses
Fewer steps needed to perform registration
and on-line correction
No manual export of portal images
No manual entry of current table coordinates
No need to print shift information to take into the
treatment room
Consolidation of daily shift information within
the EMR for better documentation

Setup Intelligence: Advantages over Acculoc
Visualization of the reference image
alongside the portal image aids in the
identification of fiducial markers
The capacity to perform and review
image registrations remotely
The ability to use fewer than 3 markers
for image registration
Useful when a “bad” marker placement of
migrated marker makes the use of 3 markers
impossible

Stereoscopic Localization Challenges
Marker Migration
~10% patients
impacted by marker
migration since 2006
Measures of
registration error
(FRE, mean error)
should be monitored
frequently
Isocenter
#1
#2
#3
???
#2
#1
#3

Obeying the “rules”
The verification images must have been
acquired within 10 minutes of each other.
10 minute time interval for image
registration starting from acquisition of
1st image
Beware of incorrect time-stamped
images!

Marker Imaging
Imaging with the
graticule in place can
obscure implanted
markers
MOSAIQ can
perform portal image
scaling manually or
automatically using
field edge matching

Quality Assurance
Acceptance of image
registration software:
End-to-end test of
CT image acquisition
TPS handling
Portal image acquisition,
Import/export handling,
Marker localization and shift
calculation,
Couch translation

IGRT Implementation and QA
Advanced technologies require new
paradigms, training, QA procedures
Therapist procedures
Patient shift action levels
Physician approval protocol/documentation
Physics QA procedure
Longer patient treatment slots (?)

Patient Shift Action Levels
If the shift is <= 3mm, no couch move
necessary
If the shift is >3mm but <=8mm, move couch
as directed. No verification image needed.
If the shift is > 8mm but <=15 mm, move couch
as directed. Acquire verification films. Repeat
localization as above.
If the shift is >15mm. Notify
physics/physician.
* CTV-to-PTV = prostate + 7mm/5mm posterior; IMRT treatment planning

IM-IGRT Imaging Dose: Modality Comparison
Ex. Pelvic RT
Dose estimated for 30 fraction w/at least once daily imaging
0.7 Gy*0.75 cGy2.1 Gy
kV CBCT (full
rotation, 120 kVp,
660mAs)
kV portal imaging
(orthogonal ports, 120
kVp, 2 mAs/field)
MV portal imaging
(orthogonal ports,
4MU per)
* Twice a day imaging would result in accumulated dose > 1Gy
Med. Phys. 33, (6), June 2006

IGRT Billing
Stereoscopic X-ray Guidance: CPT 77421
Images fused and registered
Customized software used to calculate shifts
Shifts made
Professional and technical component
MD work has to be documented
Documentation and Billing of IGRT
David Beyer – ASTRO IGRT Symposium 2008
http://www.astro.org/meetings/UpcomingMeetin
gs/IGRTSymposium/ScientificProgram/document
s/BeyerD.pdf

Localization Trend Review
Documentation of On-line Correction

Image Review/Approval
Daily Patient Offsets
Image Review/Approval
“OK to treat after shift as calculated by localization software.”

E-chart Notes
“OK to treat after shift as calculated by localization software.”

Documenting Third-Party Offsets
ACCULOC Localization Third-Party Offset

Summary
IM-IGRT helps reduce interfraction and setup
errors to ~2 mm, providing the quality
assurance needed for IMRT and dose
escalation
An IM-IGRT protocol in combination with
appropriate margins provides improved
dosimetric accuracy in prostate RT over
uncorrected protocols
Setup Assist/Intelligence provides a practical
and accurate means of performing on-line
setup correction

SupportPlus Resources
Documentation/Videos
Image Registration I
Image Registration II
Setup Intelligence
Top 10 Radoc Support Questions

SpecialSpecialSpecialSpecial
ThanksThanksThanksThanks
Robin McCaw – Elekta/IMPAC
NCBH Therapists &
Dosimetrists
Phillip Smith

Prostate IGRT With Setup Intelligence 4sharing

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