Download Treatment Quality Assurance for Linac Based SRS/SBRT

Treatment Quality Assurance
for Linac Based SRS/SBRT
Fang-Fang Yin, PhD
Duke University Medical Center
SEAAPM 2011, Myrtle Beach, SC
Acknowledgements
• SEAAPM Symposium Organization Committee
– especially to J. Daniel Bourland, PhD
• SRS/SBRT Team at Duke
• Duke University has a research agreement with
Varian Medical Systems
SRS and SBRT
Radiation therapy with a single fraction high
dose or a few hypo-fractionated prescription
doses to lesions.
The challenge for SRS and SBRT is to accurately
and precisely deliver conformal high dose
radiation to the target and minimize normal tissue
damage.
Process for Image-Guided SRS/SBRT
Case selection
Assessment
Immobilization
Onboard imaging
3/4-D simulation
Treatment
N
3/4-D planning
Onboard vs. Reference
Correction?
Patient setup
Onboard imaging
Y
General Processes for SRS/SBRT
• Patient process
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–
–
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–
–
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Consultation
Immobilization/imaging
Planning/prescription
Patient specific QA
Localization
Delivery
Motion management
Real-time verification
Treatment assessment
• Physics process
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–
–
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Beam data
QA: Safety
QA: daily, radiation / IGRT
W-L testing
Dose calculation
QA device QA
Beam calibration
An Integrated Treatment Process
SBRT Practice Guidelines: AAPM TG 101
Process QA: Quality/Risk Factors
• Program development
– Infrastructure
• Equipment: hardware and software
• Instrumentations
– Procedures and policies (what and how to do from
patient in to out)
• The team untrained/unqualified
– Physician
– Physicist
– Other staff: therapists, nurses, …
QA Programs for a SRS/SBRT Unit
Duke Center for
SRS/SBRT
(Novalis Tx)
• Procedures and policies
for SRS/SBRT
• QA for delivery system
• QA for imaging system
• QA for planning system
• QA for immobilization
device
• QA for patient specific plan
(i.e., IMRT/VMAT)
• QA for record & verifying
system
• QA for match software
• QA for gating system
• QA for 6D couch
• ……
Use Case: Delivery Leaf Width
Relative Volume (%)
5 mm
2.5 mm
5 mm
2.5 mm
0
10
20
30
40
50
60
70
Relative dose (%)
80
90 100 110
Duke Univ. 2008
Process QA: Quality/Risk Factors
• Skip some procedures
– Consultation: case was not discussed between
physician and physicist. At the time of imagng,
not sure how to position patient …
• Not properly immobilized and not enough anatomy
was included in images. As a result, patient resim
and suboptimal positioning
• Rushing to get patient treated and to be
told QA may be done after first treatment
AAPM TG 101 Recommendation:
SBRT Patient Selection Criteria
•
•
The most effective way: participation in formal group trials;
whether single-institutional or multi-institutional trials
sponsored by the NCI or other sources, or through NCIsponsored cooperative group trials such as those of the
RTOG.
When appropriate protocols are not available, clinicians
must decide whether they will treat patients in accordance
with published guidelines or develop new SBRT
guidelines. At a minimum, an institutional treatment
protocol or set of guidelines should be developed by
radiation oncologists and physicists.
General QA Guidelines
•
•
•
•
•
•
•
•
•
•
AAPM TG 40
AAPM TG 56 SRS, 58 EPID
AAPM TG 101
AAPM TG 104
AAPM TG 119
AAPM TG 142
AAPM TG 75, 76
ASTRO TGs, reports
ACR guidelines
….
Performance QA: Physics Process
Daily machine warmup
Daily, Monthly, annual QA (TG142)
Additional:
WL test (combined with daily IGRT)
Patient specific QA
chart checking
MU calculation
IMRT/VMAT QA
Time-out at machine
Physicist/physician presence
check list and sign off sheet
Patient Specific QA
IMRT QA
Patient Specific QA
VMAT QA
Performance QA: Quality/Risk Factors
– W-L testing: what if BB is off center?
QA Consideration for QA Phantoms
How to select:
Daily QAphantom
phantom
Imaging
Block Tray
Dosimetry phantom
CT phantomIMRT phantom
4D motion phantom
Tissue phantom
• Purpose
• Multiple purposes
• Accuracy
• Ease of use
• Simplicity
• Size and weight
• Quality
• Cost
• …..
• Maintenance
QA Considerations for QA Devices
Films
Detectors
Electrometers and cables
Analysis software
Beam data scanner
How to
• Acceptance testing
• Functionality
• Calibration
• Maintenance
• …..
Clinical Needs of QA Phantoms
• For existing QAs:
–
–
–
–
Accurate and simple
Multi-task with analysis tool
Proper size and efficient
Easy to do and analysis
• For emerging QAs:
–
–
–
–
4D MRI
Proton
4D gated treatment
……
Process QA: Immobilization
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Patient movement
Organ motion
Patient comfort
Reproducibility
Effort to positioning
Accuracy
Simulation time
Beam orientation
Localization Imaging
Head and Body Immobilization
“Frameless” SRS/SBRT?
• Immobilization
– Invasive frame: pins, metal devices, etc.
– Non-invasive frame: Bodyframe, BodyFix
– Constraints: alpha cradle, vacuum bag, etc.
• Geometric correlation between patient and
machine coordinates
– On-board imaging and fusion (IGRT)
– Mechanical (Constraints): Localization rods and
distance measures
– Visual: Measurements, laser, skin marks
Recommendation for Patient Positioning,
Immobilization, Localization and Delivery
• For SBRT, image-guided localization techniques shall be
used to guarantee the spatial accuracy of the delivered dose
distribution with a high confidence level.
• Body frames and associated fiducial systems may be used
for immobilization and coarse localization; however, they
shall not be used as a sole localization technique.
• To maintain the spatial accuracy throughout the treatment
delivery through either integrated image-based monitoring
systems or through aggressive immobilization of
appropriate targets, such as the spine.
AAPM TG101
AAPM TG 101 Recommendation:
Simulation imaging
Regardless of imaging modality, simulation of the
patient should take place with the patient in the
treatment position.
The simulation study should cover the target and all
organs at risk to obtain geometric and dosimetric
information for the treatment setup.
Slice thickness: < 3 mm near clinically important organs
Process QA: Planning
• Planning/prescription
– Delivery technique, choose after simulation, KISS
– Targets and organ at risk volumes, skin, chestwall,
lung low dose volume
– Previous treatment
• Contour accuracy
– Image fusion, positioning difference, imaging system
accuracy
– Contour deviation
– Margin for SRS, GTV-PTV: 1 mm, 2 mm, 3 mm….
Treatment Planning Recommendation
• The adequacy of target margins i.e., GTV, CTV, ITV, in
SBRT should be based on
– understanding of how the steep dose gradients
– high fractional doses of SBRT affect the accuracy of traditional
margin recipes
– the natural history of the tumor
– the limitations of in-house localization capabilities to reduce
random and systematic treatment uncertainty
– from information in the current literature
• Simultaneously, centers should make systematic efforts
to gather and analyze clinical results to improve margin
design in the future
AAPM TG101
Normal Tissue Dose Tolerance
TG 101 Recommendation:
Normal tissue dose tolerances in the context
of SBRT are still evolving and only a limited
experience exists from which to draw
recommendations. Except in the setting of
IRB approved Phase I protocols, critical organ
tolerance doses based on the SBRT
experience in the evolving peer-reviewed
literature must be respected.
Dose Calculation Algorithm
• Recommendation: Algorithms that account for 3D scatter
integration such as convolution/superposition have been
found including by the RPC study to perform adequately
in most clinical situations, including in many cases
circumstances where there is a loss of electronic
equilibrium such as the lung tissue interface or tumor
margin in low-density medium.
• Calculation algorithms accounting for better photon and
electron transport such as Monte Carlo would be ideal for
the most demanding circumstances, such as a small
lesion entirely surrounded by a low-density medium.
AAPM TG101
AAPM TG 101: Motion Management
AAPM Task Group 76 describes the various tumor-motion
strategies in detail. Techniques to image moving targets
include slow CT breath-hold techniques, gated approaches,
4DCT used in conjunction with MIP, minimum intensity
projection and respiration-correlated PET-CT.
If target and radiosensitive critical structures cannot be
localized on a sectional imaging modality with sufficient
accuracy because of motion and/or metal artifacts, SBRT
should not be pursued as a treatment option.
Recommendation for Moving Target
For all SBRT patients with targets in the thorax or abdomen,
a patient-specific tumor-motion assessment should be
available. This serves to quantify the motion expected
during the respiratory cycle. This data may then be used
a) To determine if the patient’s treatment would likely benefit
from techniques such as respiratory gating;
b) To quantify the residual motion expected during the
respiratory gated delivery if such delivery is used;
C) To design margins for treatment planning; and
D) To quantify and account for any phase shift between
Process QA: Discrepancy of
Contours from Different Images
ITV discrepancy
Performance QA: Quality/Risk Factors
Physics dosimetry measurement:
– Beam data
– Profile
– PDD
– Output factor
Detector 2
Detector 1
Small Field Dosimetry Error
From 0.65Æ0.32
Ion
chamber
Yin et al Med. Phys. 2002
Special Dosimetry Recommendation
Due to the small dimensions and steep dose
gradients of photon beams used in SRS/SRT and IMRT,
an appropriate dosimeter with a spatial resolution of
approximately 1 mm or better stereotactic detectors is
required to measure the basic dosimetry data, e.g., the
total scatter factor or relative output factor, tissuemaximum ratio, and off-axis ratios. Even with
stereotactic detectors, careful detector-phantom setup,
and detailed dose corrections, one might still find more
than 10% discrepancies among the measurements of
very small fields (<10 mm in diameter)
AAPM TG101
Process QA: Quality/Risk Factors
• Verification procedures
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–
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Patient position
Target localization
Motion checking
….
• Image guidance
– Method
– technique
IGRT Case: Intra-Fraction Imaging
Example of dual x-ray imaging
IGRT Case: 2D and 3D for Liver Tumor
CBCTs
2-D Images
On-Board Imaging
IGRT Case: 3-D CBCT Free-Breath ITV
CBCT
images
after
correction
CBCT
images
prior
to
correction
Planning
CT with
target
contours
Post-treatment
CBCT
Wang et al Ref J 2007
IGRT Case: Image Analysis Tool
Bladder in
planning CT as
contour overlay
Daily Bladder
as image
In-room CT
Hardware
and
software
application
and
verification
Bony Structure is off
Variable rectal filling
observed
In-room CT
Prostate target is aligned with
the CT image
Reference CT
TG 104 2008
IGRT Case: CBCT for Brain
Onboard verification
Plan
Imaging Device Inaccuracy
5 mm shifts
Yin
Risk Factors in IMRT/VMAT/IGRT
Original
2 cm Mis-P
2 cm Mis-P
2 cm Mis-P
5% U-Dose
Original
5% U-Dose
Original
5% U-Dose
PTV54: 7mm from CTV
PTV76: 5mm from CTV
Yin
Anatomic Surrogate Imaging:
Soft Tissue Organ and Isodose
Planning CT
50Gy
40Gy
CBCT
Recommendation for Treatment
•
At least one qualified physicist be present from the
beginning to end of the first treatment fraction.
•
For subsequent fractions, it is recommended that a
qualified physicist be available, particularly for patient
setup in order to verify immobilization, imaging,
registration, gating, and setup correction.
•
Radiation therapists be well-trained in SBRT procedures.
•
A radiation oncologist approve the result of the image
guidance and verify the port films before every fraction
of the SBRT treatment.
AAPM TG101
A Clinical Case for Integrated
Respiratory Gated Treatment
Verification for Liver Cancers
What Critical Information Is Needed
for Verifying Gated Treatment of Liver?
• Target to be verified
• Tumors
• Surrogate to the target
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•
•
•
•
Anatomical marker
Implanted marker
Verification of surrogate
Imaging
Motion correlated signal
Liver case: Target-Surrogate
Implanted
marker
Rt lobe PTV
112.1 cm3
Lt lobe PTV
35.3 cm3
Anatomical
surrogate
(diaphragm)
Implanted Surrogate: Marker
• Implant a X-Mark fiducial marker during the biopsy
• Ultrasound guided implantation in radiology department
• 0.85 mm x 1 cm in a pre-waxed introducer needle (18 GA)
• Simulation after one week
Imaging Modality
CT-kV
FluoroTRUS-MRI
0.45 mm
Y
Y
0.85 mm
Y
Y
Y
Y
Y
Diameter
1.15mm
EPIDPortal-MV
Imaging: Immobilization & CT Simulation
• Immobilization: dedicated alpha cradle
• Imaging studies:
– Free-breathing CT – define imaging range
– 4D CT acquisition – phase-gated with RPM
• Sorted by 10 phase intervals
– Verification by fluoroscopic
imaging - visually
– MRI images with breath-hold
Motion Correlated Treat: Beam Design
• Draw GTV in all 10 phase images (MIP images)
– Overall motion: 1.5 cm
• Draw GTV between 30-70% phase images (MIP images)
– Motion <= 5 mm
Localization Techniques
• OBI orthogonal images – within phase window
• CBCT images – ITV – not in phase window
• Real-time portal imaging – tracking of markers
• Verification surrogates:
– Rt lobe lesion – implanted marker
– Lt lobe lesion - diaphragm
Create Verification Fields
Rt Lat Field
for Right Lobe
Lesion
50% phase window
Free-breathing
Create Verification Fields
Anterior Field
for Left Lobe
Lesion
50% phase window
Free-breathing
Target Localization – Orthogonal Imaging
Right lob lesion
Phase-gated OBI images
Target Localization for ITV– CBCT
Right lobe lesion
Free-breathing CBCT
Verification of Gating Windows –
Fluoroscopic Imaging
Gating window
Right lobe lesion
Verification of Gating Windows –
Fluoroscopic Imaging
Left lobe lesion
Rt Lat Setup Field
Ant Setup Field
Treat Verification of Implanted
Surrogate – Cine Portal Imaging
Right lobe lesion
Treat Verification of Anatomical
Surrogate – Cine Portal Imaging
Left lobe lesion
Clinical Implementation of SRS/SBRT
•
•
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Establish the scope of the program including a selection of treatment
sites and the clinical goals for each site.
Determine a treatment modality, dose-fractionation scheme, and
treatment planning goals target definition, target coverage, conformity
index, etc. that support the clinical goals for each treatment site.
For each treatment modality and treatment scheme, determine the
equipment requirements for patient positioning, treatment delivery, and
verification.
Determine personnel needs for implementation and maintenance.
Establish and perform acceptance and commissioning test procedures
for the equipment.
Establishing simulation, treatment planning, delivery and verification
guidelines, reporting methodology and routine QA procedures, and
Conducting personnel training.
Summary
• Each SRS/SBRT deserve special attention
• Accuracy and precision is critical
• QAs should be implemented as an
integrated process
• Both individual and systematic factors
should be considered for the QA process
• End-to-end test is a critical procedure
Thank you!
Quality Assurance Program
• A program that is designed to control and
maintain the standard of quality set for that
program
• In radiation oncology, it is essentially a set of
policies and procedures to maintain the
quality of patient care
• The general standards and criteria of QA are
usually set collectively by the profession