Download SBRT: AAPM Task Group 101 Report

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SBRT: AAPM Task Group 101 Report
Kamil M. Yenice, Ph.D.
University of Chicago
Department of Radiation Oncology
An Introduction to the
Recommendations for
Physicists and Physicians from
the AAPM Task Group No.
101….. Benedict, et al Medical
Physics (2010)
Major Topics Covered in TG101:
1. History and Rationale for SBRT
2. Current status of SBRT patient selection
criteria
3. Simulation Imaging and Treatment Planning
4. Patient Positioning, Immobilization, Target
localization, and Delivery
5. Special Dosimetry Considerations
6. Clinical Implementation of SBRT
7. Future Directions
What is SBRT?
•  SBRT refers to the precise irradiation of an
image defined extra-cranial lesion associated
with the use of high radiation dose delivered in a
small number of fractions. (NCAT-UK definition)
•  In SBRT, confidence in this accuracy is
accomplished by the integration of modern
imaging, simulation, treatment planning, and
delivery technologies into all phases of the
treatment process; from treatment simulation
and planning, and continuing throughout beam
delivery (TG 101)
So What is SBRT?
Image Guidance
SBRT
Stereotactic
Radiosurgery
Slide: Courtesy of Stanley H. Benedict, PhD
IMRT and
Conformal
3D Delivery
Conventional RT vs. SBRT
Characteristic
Conventional RT
SBRT
Dose / Fraction
1.8 – 3 Gy
6 – 30 Gy
No. of Fractions
10 – 30
1-5
Target definition
CTV / PTV
GTV / CTV / ITV/
PTV
well-defined tumors:
GTV=CTV
Margin
gross disease +
clinical extension:
tumor may not have a
sharp boundary.
Centimeters
Millimeters
(From Table 1: AAPM TG 101)
Although SBRT employs similar basic principles as in conventional modalities
including IMRT and IGRT, its extreme hypofractionated treatment delivery demands
the utmost consideration for safety!
Frame Based Immobilization and
Localization Systems
Frame systems provide a link
between patient immobilization
and localization: accurate
localization relies on patient setup
reproducibility.
Assumption: variations in the
stereotactic location of the target
are due only to organ motion and
not to setup uncertainties.
Not true for most situations!
Frame Based Immobilization and
Localization Systems
Frame systems provide a link
between patient immobilization
and localization: accurate
localization relies on patient setup
reproducibility.
Assumption: variations in the
stereotactic location of the target
are due only to organ motion and
not to setup uncertainties.
Not true for most situations!
Patient Positioning, Immobilization, Target
Localization, and Delivery
Recommendation (TG 101):
• Body frames and fiducial systems are OK for
immobilization and positioning aids
• They shall NOT be used as a sole localization technique!
Recommendations (TG 101)
Targeting: For SBRT, image-guided localization
techniques shall be used to guarantee the spatial
accuracy of the delivered dose distribution with a
high confidence level.
The patient position should be monitored during
the entire treatment and any deviations in
treatment/target position as assessed from
available visual, optical, and radiographic tools
such as repeat imaging should be recorded for
the entire treatment duration.
IGRT Technology for SBRT
Commissioning of a SRS Program
“Quality and Safety Considerations in SRS and SBRT”, Solberg et al, Practical Rad Onc, 2011
SBRT Commissioning (I)
•  “Commissioning tests should be
developed by the institution’s physics team
to explore in detail every aspect of the
system with the goal of developing a
comprehensive baseline characterization
of the performance of the
system.” (TG-101)
SBRT Commissioning (II)
Quality Assurance of Radiation Therapy and
The Challenges of Advanced Technologies
Symposium (Supplement to IJROBP: 2008)
•  The modified Winston-Lutz test should be performed at the time any
SBRT system is initially commissioned, and it should be repeated monthly.
•  All SBRT procedures should include detailed information on how the
registration software is to be applied.
•  Special moving phantoms should be used to demonstrate that gating and/
or tracking techniques are accurate.
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
MiMi Phantom (Standard Imaging)
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Isocenter Coincidence Testing
Bissonnette et al, Int J Rad Oncol
Biol Phys, 71(1) S57–S61, 2008.
MiMi Phantom Axial CT Scans
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Center Phantom in MV Isocenter
by Imaging at 4 Gantry Angles
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Measure Offset to kV Isocenter
by 2D/2D Match at 4 Angles
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Measure Offset to CBCT Isocenter
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Measure Offset to Laser Isocenter
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
Root Mean Square Distances of IGRT
Isocenter Offsets
Trial number
Trilogy couch precision: a factor in larger offset values
Slide: Courtesy of Hania Al-Hallaq, PhD, Univ. of Chicago
TG-142: Imaging & Treatment Isocenter Coincidence
Daily IGRT QA-Varian System
UCMC Daily Imaging QA
Distance Error Criterion: ≤ 1 mm (TrueBeam)
≤ 2mm (C-series)
SBRT Planning Issues
Simulation with Motion or Imaging Artifacts
Recommendation: If target and/or critical
structures cannot be localized accurately due
to motion or metal artifacts……
STOP!
Do NOT pursue SBRT as a treatment option!
Respiratory Motion Management
Recommendation: For thoracic and abdominal
targets, a patient-specific tumor motion
assessment is recommended.
• Quantifies motion expected over respiratory cycle
• Determines if techniques such as respiratory gating
would be beneficial
• Helps in defining margins for treatment planning
• Allows compensation for temporal phase shifts
between tumor motion and respiratory cycle
SBRT Target Margins
Recommendation: At the current time, it
remains difficult to base target margins directly
on clinical results. The adequacy of ICRU
definitions depend on:
• Understanding of how high absolute doses and
sharp dose falloffs affect accuracy
• Limitations on in-house localization uncertainty
• Guidance from current peer-reviewed literature
Make an effort to gather and analyze your own
clinical results to improve margin design!
Normal Tissue Tolerances
Recommendation: Normal tissue dose
tolerances in the context of SBRT are still
evolving. So…. CAUTION!
• If part of an IRB-approved phase 1 protocol,
proceed carefully
• Otherwise, the evolving peer-reviewed literature
must be respected!
Table of Normal Tissue Tolerances
TG 101: Table 3
Table of Normal Tissue Tolerances
• There is sparse long-term follow-up for SBRT.
• Data in table 3 should be treated as a first
approximation!
• Doses are mostly unvalidated, but doses
are based mostly on observation and theory.
• There is some measure of educated
guessing!
R. Timmerman, 10/26/09, pers. comm.
Biological Effects
• NOT the same as traditional
radiation therapy!!!!
• Cannot extrapolate from the linear
quadratic model!!!!
Biological Dose Equivalents
Total Physical
Dose (Gy)
NTD10
(Gy)
Log10 Estimated 30 mo local NTD
3
Cell Kill progression-free
(Gy)
survival
30 x 2 = 60*
(in 6 weeks)
65
9.9
17.7 % (w. repopulation)
60
35 x 2 = 70*
(in 7 weeks)
72
10.9
28.4 % (w. repopulation)
70
4 x 12 = 48
83
12.6
78.9 % (no repopulation)
144
3 x 15 = 45
94
14.2
90.8 % (no repopulation)
162
5 x 12 = 60
110
16.7
97.1% (no repopulation) 180
3 x 20 = 60
150
22.7
>99% (no repopulation)
276
3 x 22 = 66
176
26.7
>99% (no repopulation)
330
* NTD = Normalized Tissue Doses estimated using an α/β of 10 (late) an 3 Gy (early)
Quantitative Analyses of Normal Tissue Effects in
the Clinic (QUANTEC Study)
IJROBP Vol 76, No 3, Supplement (2010)
Summary of SRS/SBRT Normal Tissue Tolerances
SBRT Participation In Trials
Recommendation: The most effective way to
further the radiation oncology community’s
SBRT knowledge base is through participation
in formal group trials
• Single- or multi- institution
• Ideally NCI-sponsored or NCI-cooperative groups
(e.g. RTOG)
• If no formal trial, look to publications
• If no publications, structure as internal clinical trial
RTOG SBRT Protocols
•  0631 Spine
•  0813 and 0915 Lung
•  0438 Liver
Provide guidelines for treatment planning:
Dose Prescription
Target Coverage
Dose Constraints
Example Plan: Spinal SBRT with IMRT
Bowel sparing
Low peripheral
dose
Sharp dose gradient
Evaluate the effect of setup/motion on delivered dose!
Know the limitations of your dose algorithm!
(Pay attention to warnings in user’s manual)
This vendor safety notice warns against two specific issues for
potential inaccurate dose computation due to:
1.  Use of conditions that require extrapolation of data beyond
measurement range
2.  Use of large grid size resulting in unexpected results for
small structures
Recommendation (TG 101): SBRT commonly includes
extremely high-dose gradients near the boundary of the
target and often makes use of IMRT techniques. This
report recommends the use of an isotropic grid size of 2
mm or finer. The use of grid sizes greater than 3 mm is
discouraged for SBRT.
Develop checklists for your program.
Sample Checklist for SRS Program: Lung
“Quality and Safety Considerations in SRS and SBRT”, Solberg et al, Practical Rad Onc, 2011
Checklist for SRS Planning Treatment Delivery (UC)
Use a Dry Run Before Patient Treatment
•  Treatment verification
– Reproduce setup
– Verify isocenter
– Clinically mode up each treatment field
 Check beam clearance (collision)
 Check any interlock
  MLC interlock? Reinitialized but can not clear means
corruption of MLC files undeliverable beam
  Potential MU problem? For example > 1000 for any
single field beyond machine capability for non-SRS beams
Clearly mark immobilization devices after successful dry run.
SBRT Dose Verification with Scintillator
1.  Cast the plan in a
phantom.
2. Deliver all the
beams under
treatment
conditions.
3. Verify the composite
dose with a
scintillator dosimeter
Exradin W1 Scintillator from Standard Imaging
Courtesy of Tianming Wu, PhD
SBRT Patient Dose Verification with
Scintillator
Slide: Courtesy of Tianming Wu, PhD
IGRT for SBRT Lung/Liver/Abdominal Cases
•  If no implanted fiducials, create fluoro beam
aperture that hugs GTV.
•  If there is fiducials, create fluoro beam aperture
that use fiducials as corners.
•  CBCT alignment with GTV, bony landmark
secondary but should be less than 1cm
discrepancy. Otherwise, reposition patient.
•  CBCT sometimes do not align well with
averaged sim CT due to breathing variation
•  Fluoro to verify positioning after CBCT.
•  Fluoro between fields to monitor setup
consistency.
TG-101: Physicist Presence
Single-Fraction SRS
Physicist present for entire
procedure
Multiple-Fraction SRS
Physicist present for 1st
fraction and at setup of
remaining fractions
SBRT
Physicist present for 1st
fraction, and setup for
every fraction to verify
imaging, registration,
gating, immobilization
•  UC Physics Team
–  Hania Al-Hallaq, PhD
–  Karl Farrey, MS
–  Hyejoo Kang, PhD
–  Ji Li, PhD
–  Julien Partouche, MS
–  Chester Reft, PhD
–  Chris Stepaniak, PhD
–  Rodney Wiersma, PhD
–  Tianming Wu, PhD
–  Bradley McCabe, PhD
–  Laura, Padilla, PhD
Stanley H. Benedict, PhD
Univ. of California- Davis
Linac Vendor’s Isocenter Test
Set of 63 image Shots (Gantry, Coll., Couch)
Specifications:
Gantry-Collimator Isocenter Offset ≤0.50 mm (0.30mm)
Gantry-Collimator-Couch Iso Offset ≤ 0.75mm (0.61mm)
TrueBeam: MV-kV Coincidence Test
BB for MV Imaging
CBCT Phantom with
Markers
kV-MV isocenter coincidence ≤ 0.5 mm
Typical results < 0.2 mm
UC Linac Isocenter Accuracy Test
(using a similar system for Lutz test)
In-house Matlab code
(Ji Li, PhD – UC)