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Mooooo
Stereotactic Radiosurgery - State of the Art
Technology and Implementation: Quality
and Safety Aspects of Linac Delivery
Timothy D. Solberg, Ph.D.
Barbara Crittenden Professor of Cancer Research
Director, Division of Medical Physics and Engineering
Department of Radiation Oncology
University of Texas Southwestern Medical Center
Timothy.solberg@utsouthwestern.edu
Therapy Course WE-A(SAM)-BRCD-1
Define your radiosurgery program goals before you begin
Assemble all the resources needed to achieve your
goals before you begin
Information
People
Equipment
Time
Where to Start? Define Your Program Goals!
Mets Only?
Benign?
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Where to Start? Define Your Program Goals!
AVM?
Mets Only?
Benign?
DSA?
Where to Start? Define Your Program Goals!
AVM?
Mets Only?
Benign?
Rotational Angio?
Where to Start? Define Your Program Goals!
Trigeminal Neuralgia? Other Functional?
Small Detector(s)
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Single fraction or fractionated?
Frame-based
OR
Frameless (Image-Guided)
SBRT?
Where to Start? Get the Documentation
AAPM Efforts
TG
TG
TG
TG
TG
42 – Stereotactic Radiosurgery
68 – Intracranial Stereotactic Positioning Systems
101 – Stereotactic Body Radiotherapy
104 – kV Localization in Therapy
135 – QA for Robotic Radiosurgery
TG 142 – Quality Assurance of Medical Accelerators
TG 147 – QA for Non-Radiographic Radiotherapy Localization and
Positioning Systems
AAPM Efforts In Progress
TG 117 – Use of MRI in Treatment Planning and Stereotactic Procedures
TG 132 – Use of Image Registration and Data Fusion Algorithms and
Techniques in Radiotherapy Treatment Planning
TG 155 – Small Fields / Non-Equilibrium Condition Photon Beam Dosimetry
TG 178 – Gamma Stereotactic Radiosurgery Dosimetry and QA
TG 179 – QA for Image-Guided Radiation Therapy Utilizing CT-Based
Technologies
TG 194 – Simulation Training for Medical Physicists and Impact on
Procedure Outcome
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Other Efforts
Quality Assurance for Radiation Therapy: The Challenges
of Advanced Technology Symposium (2007)
ASTRO Efforts to Improve Quality and Safety
Hendee WR, Herman MG. Improving patient safety in radiation oncology. Med Phys 38(1): 78-82, 2011
ASTRO Quality and Safety White Papers
Series of 5 safety white papers
IMRT
IGRT
SRS/SBRT
HDR
Peer Review
PRO Version:
Practical Radiation Oncology 2:2-9, 2012
Full Report Available:
Written by 9 “experts”
Reviewed by 8 independent “experts”
Endorsed by AAPM, ACR, AAMD, ASRT
Reviewed by AANS, MITA, public
Acknowledgements:
James Balter
Stan Benedict
Dick Fraass
Brian Kavanagh
Curtis Miyamoto
Todd Pawlicki
Lou Potters
Josh Yamada
http://download.journals.elsevierhealth.com/mmcs/journals/1879-8500/PIIS1879850011002165.mmc1.pdf
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ASTRO SRS / SBRT* White Paper
• SRS / SBRT, the delivery of 1-5 high dose fraction, is
fundamentally different than conventional radiotherapy
in that the intent is ablative. It is as much a special
procedure as a heart or liver transplant.
• This leaves no margin for error.
• The approach to SRS/SBRT quality and safety requires:
a much more broad approach than simply preventing
technical errors
adherence to an appropriately high standard of care
in all aspects, clinical as well as technical/physical
*SRS/SBRT are often collectively referred to as SABR – Stereotactic Ablative Radiotherapy
SRS/SBRT as a well thought out program, not an addition/afterthought
Establish goals and clinical guidelines for the overall program and for
each disease site.
Identify necessary resources: personnel, expertise, technology, time.
Develop comprehensive QA processes.
Develop processes for peer review, documentation and reporting,
ongoing needs assessment, and regular review of clinical protocols.
Use checklists for all program aspects.
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Where to Start? Get the Documentation
Get the Resources
So you will need more staff!!!
Pick the appropriate device(s)
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Get the right equipment
Quality Assurance in SRS / SRT
Localization Accuracy - Can you hit the target?
Dosimetric Accuracy – Can you delivery the prescribed dose?
Imaging Requirements for SRS
• Use CT for geometric accuracy
• Use MR for target delineation
BUT….
“MRI contains distortions which
impede direct correlation with CT
data at the level required for SRS”
Stereotactic Radiosurgery – AAPM Report No. 54
Other References
TS Sumanaweera, JR Adler, S Napel, et al., Characterization of
spatial distortion in magnet resonance imaging and its implications
for stereotactic surgery,” Neurosurgery 35: 696-704, 1994.
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Axial
Coronal
Compare separation measured on
MRI with that expected
1T
1.5T
Absolute difference between CT and MR
•
•
•
Distortion is worse at the periphery of
the image
Distortion has a systematic component
– in the frequency encoding direction
Systematic component is due to the
stereotactic fidicials
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Localization Accuracy
There is a need for specialized phantoms to assess /
verify capabilities of IGRT systems
Assessment of Frame Coordinate System
Structure
Cylinder
Cube
Cone
Sphere
AP
0.0
20.0
-35.0
25.0
Phantom Specifications
LAT
VERT
0.0
30.0
-17.0
40.0
-20.0
40.0
20.0
32.7
iPlan Stereotactic Coordinates
AP
LAT
VERT
1.0
0.4
30.8
20.8
-17.1
42.4
-34.6
-19.7
40.8
25.5
20.2
33.5
Assessment of Frame / Coordinate-based System
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Assessment of Frame /
Coordinate-based System
What About Image Guidance?
Image Guided End-to-End Assessment
DEPT OF RADIATION ONCOLOGY
Dana Dawson dana@imt.ms
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Hidden Target Evaluation
Repeated 50 times
Average 3D displacement
1.11 mm
± 0.42 mm
Image Guided End-to-End Assessment
3D error 1.1 ± 0.3 mm
3D error 1.2 ± 0.4 mm
Chang et al, Neurosurgery 2003
Repeat for CBCT Localization
Axial
Sagittal
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Hidden Target Evaluation
Everything works well in phantoms
Does it work in patients?
Frame Case
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Frameless Case
Results of Patient Data
Single
Fraction
n = 35
Multiple
Fraction
n = 565
(mm)
Lat.
Long.
Vert.
3D
vector
Average
-0.09
0.13
0.23
1.02
Standard
Deviation
0.67
0.57
0.76
0.59
Average
0.17
0.47
0.17
2.36
Standard
Deviation
1.24
2.11
1.03
1.32
Task Group Report 142: Quality Assurance of Medical Accelerators
Daily QA
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Daily Winston-Lutz Test
Align lasers based on W-L test
Everything else (e.g., image guidance) follows
Need to perform for cones and MLC
Need to perform after any service
Task Group Report 142: Quality Assurance of Medical Accelerators
Daily QA
On linac systems, image guidance is
becoming widely used for SRS localization
QA of IGRT Systems for SRS
Hidden Target
Phantom
Align to Lasers
Daily QA of IGRT systems, ensuring that the laser, kV
and MV axes are all coincident, is absolutely essential
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Assess Laser-kV coincidence
Hidden Target Test:
kV System
Assess kV-MV coincidence
Hidden Target Test:
MV System
Assess kV-MV coincidence
Gantry
(deg)
Table
(deg)
Measured Deviation
x (mm)
y (mm)
Hidden Target Test:
MV System
Assess kV-MV
coincidence
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Dosimetric Accuracy
Several challenges:
Measurement of small fields
End-to-end commissioning of TP system(s), combining
localization and dosimetry
Beam data acquisition for
SRS / SBRT is challenging
and time consuming
Small fields
Sharp gradients
Lots of data to acquire:
Cones
MLC
Direct Measurement
Pencil Beam
Monte Carlo
Repeat for multiple energies
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How do you know your data are good?
Compare with Literature, Other Institutions / Machines
Institution 1
▪ Institution 2
Observations
some
treatment
units: 15
mm collimator
Compare of
with
Other
Institutions
/ Machines
SRSMode
Mode12.5
15
6X
mmCollimator
Collimator
6XSRS
7.5
10 mm
6.0
6X
SRS
Mode
4.0
mm
Collimator
120
Institution 22
Institution
Institution 11
Institution
100
OAR
80
60
40
20
0
-30
-30
-20
-20
-10
0
10
20
30
30
Distance (mm)
Million $$$ question: Are the output factors correct?
Compare with Other Institutions / Machines
Circular Cones – Device A
Institution 1
Institution 2
Institution 3
Circular Cones – Device B
Institution 1
Institution 2
Institution 3
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Neurochirurgie. 56(5):368-73, 2010
33 patients with 57 brain mets
Mean volume: 3.2 cc [0.04 – 14.07]
Mean prescribed dose: 20 Gy [10 – 23]
Mean delivered dose: 31.5 Gy [13 – 52]
Mean overdose: 61.2% [5.6 – 226.8]
Local control: 80.7%
No morbidity observed
32 unilateral ACN patients
31% 12 month actuarial rate of trigeminal neuropathy
SRS treatment for a benign tumor
Overdoses ranging from 25 to 100%
Patient developed facial spasms,
balance and memory problems
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How can we prevent ……..
Thorough commissioning
Review of literature
Comparison against reference data
Beam data is good? The job is ~ half complete. Dosimetric commissioning:
Do your calculations agree with measurement?
Start simple: can your TP system reproduce your measured beam data?
Dosimetric commissioning: Do your
calculation agree with measurement?
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Comprehensive range of energy,
dose, technique, etc.
4 field box
1 isocenter
Dynamic Conformal Arcs
2 isocenters
2 isocenters
IMRT
The beam data / treatment planning system look
good (so far).
What else should I do?
End-to-End test incorporating
both localization and dosimetry
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End-to-End test incorporating both localization and dosimetry
End-to-End test incorporating
image guidance and dosimetry
Image guided dosimetric assessment
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End-to-End test incorporating image guidance and dosimetry
DEPT OF RADIATION ONCOLOGY
Dana Dawson dana@imt.ms
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Track your dosimetric results to look for systematic errors and trends
Histogram of absolute dose agreement: calculation versus measurement (n=160)
x = 0.26 1σ = 1.75
Percent Difference
Are your electronic systems configured correctly?
Planning
R/V
Do all of your commissioning
in clinical mode, and through
your R/V system
Tx Unit
Do we need to perform patient-specific dosimetry?
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Patient-specific QA
Patient Specific QA
Patient Specific QA – Clear Policies, Procedures, Checklists
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Wrong site errors are common
Event Description
Treatment Implication
Patient orientation entered incorrectly at
MR Scanner
Wrong location treated
Fiducial box not seated properly during
CT imaging
Wrong location treated
Malfunction of automatic positioning
mechanism following re-initialization
Wrong location treated
Right trigeminal nerve targeted instead
of left
Wrong location treated
Facial nerve targeted
trigeminal nerve
instead
of
Wrong location treated
Mistake in setting isocenter coordinates
Wrong location treated
Head not secured to stereotactic device
(2 events)
Wrong location treated
Selected collimators did not match
planned
Wrong
delivered
Physician mistakenly typed 28 Gy
instead of 18 Gy into planning system
Wrong dose delivered
Physicist calculated prescription to 50%
isodose instead of 40%
Wrong dose delivered
Microphone
dislodged,
stereotactic device to break
causing
Couch moved during treatment
dose/distribution
Treatment halted after 2 of
5 fractions
None; personnel interrupted
treatment
Patient Specific QA – Checklists and Timeouts!
How can we prevent ……..
Use of checklists (good practice)
Properly commissioned Record/Verify
Machine Interlocks
Backup jaws set to 40 x 40 cm2
instead of 40 x 40 mm2.
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How can we prevent ……..
Use of checklists (good practice)
Properly commissioned Record/Verify
Machine Interlocks
Backup jaws extend beyond cone
How can we prevent ……..
… a stereotactic radiosurgery (srs) collimator accessory, mfg. by brainlab, was
not inserted in the varian linear accelerator during treatment delivery. … a 5x5 cm
field was used and 6 mm cone field planned.
Brainlab provided a safety field notice in 2009 and updated use instructions in
2010. Varian provided a safety notice in 2009 and a second safety notice in 2011.
UCLA Radiation Oncology - Radiosurgery Check List:
Patient Name:
Step
1
2
3
4a
4b
5
6
7
8
9
10
11
12
13
14
15
16
17
Isocenter Operations
Arrange sheet and pad on couch.
Set the couch to 0 & coll to 90.
Take photos of patient (3).
Set backup jaws to 4.0 x 4.0cm. (2
initials & size).
Install the cone. (2 initials & size).
SINGLE FRACTION
Patient ID #:
Date:
Isocenter 1
Isocenter 2
Isocenter 3
Isocenter 4
Isocenter 5
Isocenter 6
/
/
/
/
/
/
/
/
/
/
/
/
Position isocenter templates on
positioning box. 2 init.
Enable linac switches 1, 2, and 4.
Unlock microadjusters/table locks.
Fit ring onto patient head frame.
Attach large bolts (2) onto ring.
Assist patient onto couch.
Secure frame to couch mount.
Tighten large bolts.
Attach small bolts (2) onto ring.
Secure patient to couch w/ strap.
Attach positioning box to the
frame.
Positon positioning box to the
isocenter.
Tighten Lat & Long table locks
and disable linac switches 1,2,4.
Use microadjusters, reposition box
to isocenter, lock microadjusters.
Review of fields by physician.
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Patient Specific QA – Checklists!
SRS QA is a continuing process that begins long before the
first patient is ever treated.
Establish goals, technical and clinical guidelines, policies
and procedures, for the overall program and for each
disease site, well in advance.
Failure of the QA processes has profound consequences for
SRS patients.
All stakeholders (physicians, physicists, therapists,
dosimetrists, administrators, etc.) must be committed to and
actively engaged in the QA process and ongoing quality
improvement.
Therapy Course WE-A(SAM)-BRCD-1
Measurement of dosimetric parameters of small
photon beams is complicated by:
20%
1. Loss of lateral electronic equilibrium.
19%
2. Lack of a build-up region.
20%
3. Volume averaging by small detectors.
4. Shift of dmax towards the surface for
very small beams.
5. Electron contamination due to
secondary collimators.
19%
22%
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Answer:
1. Loss of lateral electronic equilibrium.
Loss of lateral equilibrium occurs when the field
dimensions are less than the range of the
secondary electrons, results in a rapid decrease in
output factor. A small detector, ≤ 1 mm in area, is
required for small field dosimetry. In contrast,
small photon beams do exhibit a build-up region,
and while Dmax does shift slightly, it is not a
complicating factor.
Reference:
•
Benedict S, et al, “Stereotactic Body Radiation
Therapy: The Report of AAPM Task Group 101",
Med Phys 37(8): 4078-4101 (2010).
The targeting accuracy achievable with
“frameless” SRS systems is on the order of:
20%
1. 2.0 ± 0.5 mm as an end-to-end measure.
20%
2. 1.0 ± 0.5 mm as an end-to-end measure.
19%
19%
22%
3. 2.0 ± 0.5 mm as measured using a
Winston-Lutz test.
4. 1.0 ± 0.5 mm as measured using a
Winston-Lutz test.
5. Depends on whether the system uses 2D
or 3D image guidance for localization.
Answer:
2. 1.0 ± 0.5 mm as an end-to-end measure.
With modern image guidance systems, targeting accuracy in
an end-to-end sense (scan, plan, localize, assess) is on
the order of 1.0 ± 0.5 mm. This is true whether
stereoscopic x-ray imaging or CBCT is used.
References:
• SD Chang et al, “An analysis of the accuracy of the
CyberKnife: a robotic frameless stereotactic
radiosurgical system,” Neurosurgery 52(1):140-6 (2003).
• TD Solberg et al, “Quality assurance of immobilization
and target localization systems for frameless stereotactic
cranial and extracranial hypofractionated radiotherapy,”
IJROBP, 71(1):S131-S135 (2008).
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Which of the following is TRUE regarding MR
distortion in radiosurgery?
21% 1. MRI distortion is solely a random phenomenon
2. MRI distortion is constant throughout the image
field of view
3. Systematic MRI distortion occurs in the
20%
frequency encoding direction
4. Use of a stereotactic MRI localizer can correct
19%
systematic distortion
5.
MRI distortion is the same for all MR
19%
sequences
21%
Answer:
3. Systematic MRI distortion occurs in the
frequency encoding direction
References:
• Y Watanabe et al, “Geometrical accuracy of a
3-tesla magnetic resonance imaging unit in
Gamma Knife surgery,” J Neurosurg. 105:190193 (2006).
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