How Should We Verify Complex
Radiation Therapy Treatments ?
Chair: M Oldham
• “Lessons learned from 10 years of the RPC credentialing service”
– Geoff Ibbott PhD, MD Anderson Cancer Center,
• “Comprehensive verification: the role of 3D Dosimetry”
– Mark Oldham PhD, Duke University Medical Center
• “EPID verification: 2D and 3D, ex-vivo and in-vivo”
– Ben Mijnheer PhD, The Netherlands Cancer Institute,
• “Verification by independent computer algorithms, and Monte Carlo”
– Tim Zhu, University of Pennsylvania,
Learning objectives:
• to gain insight into the dosimetric challenges posed by
advanced radiation treatment techniques
• to appreciate the importance of comprehensive treatment
verification to patient safety
• to understand the rationale and capabilities of dosimetry
techniques for comprehensive treatment verification, both
in-vivo and ex-vivo
The following slides are preliminary, and will be updated as
necessary. Handouts may become available for lectures 1 and 4.
Rationale for 3D ? – catch more errors …
How should we verify complex
radiation therapy treatments ?
Comprehensive verification: the
role of 3D Dosimetry.
• RPC data
– PTV dose ≤ 7%
– Gradient ≤ 4 mm
30%
• What percentage of 168 Institutions failed criteria ???
PTV Dose
Mark Oldham, PhD, FAAPM
Associate Professor
Radiation Oncology and Biomedical Engineering
Duke University Medical Center, NC, USA
Further rationale - 2D QA does not correlate with 3D
Gradient
Outline
• Part I
– Review (partial) of 3D Dosimetry Techniques
• Several methods for accurate 3D dosimetry
• Common limitation: clinical interpretation ?
• Part II
– How to make QA data more clinically relevant ?
• 3D dosimetry has unique potential
• Take-home messages
– 3D dosimetry works and should be used
– Can follow up errors detected from routine dosimeters
– Unique advantage: QA can yield clinical interpretation
1
Partial Review of 3D dosimetry systems ?
Material
Read-out
• Polymer gels
MRI
• Radiochromic gels
– FX-orange
X-ray-CT
• Radiochromic plastics
– Presage
Optical-CT
Liquid scintillators
Transit dosimetry - EPIDS
Semi-3D systems - diode arrays
Polymer Gels
• The first 3D dosimeters (1993)
– Water, gelatin, BIS, acrylamide
• Succession of improved formulations
– Less toxic (acrylamide substitutes)
– Less oxygen sensitivity (MAGIC)
Schreiner et al., IC3DDose 2010
• Mature, well understood ..
– Non-resuable ..
– MRI - expensive but useful
– Optical-CT - scatter ?
– X-ray-CT – noise ?
Baldock et al. 55 (5) Phys Med Biol. 2010
Wuu et al., IC3DDose2010
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY
Optimizing the multiple spin echo sequence
NOT OPTIMAL
S
Image artifacts: Temperature drift
S
OPTIMAL
Si
TE1
TE2
TE3
TE4
T 2
TE
T 2
TE
2.5
2
T2
R2
R2
R2 map
1.5
1
GEL DOSIMETER:
CORONAL
(scanned)
TPS: Pinnacle
0.5
Dose map
R2 [s-1]
Dose [Gy]
Calibration plot
Yves DeDeene: IC3DDose 2010
GEL DOSIMETER:
CORONAL
reconstructed from
TRANSVERSE slices
D
0
TPS: TRA
GEL: TRA
2.5
2
1.5
SSE requires 24 acquisitions
to obtain the same SNR as
a MSE with 32 echoes !!
1
0.5
0
TPS: SAG
GEL: SAG
Yves DeDeene: IC3DDose 2010
2
Optical Tomography (optical-CT)
Comparison of Transverse Dose Distributions
(40, 60, 100, 115%)
Red: Plan Blue: Gel
Green: Film
MGS OCTOPUS Scanner
MGS Research
• Single scanning laser
– Accurate, less sensitive to scattered light
– Slow requiring many hours for high-resolution 3D
Wuu et al, IC3DDose2010
Comparison of Coronal Dose Distributions
Red: Plan
Blue: Gel
Green: Film
Wuu et al, IC3DDose2010
Brachytherapy measurements
(from Massillon et al PMB 2009)
Brachytherapy dosimetry using
BANG gel and a 100 um pixel laser
scanner (at NIST)
Courtesy of MGS Research
230 MeV Protons:
BANG vs Ion Chamber
(from Zeidan et al 2010)
Courtesy of MGS Research
Courtesy of MGS Research
3
X-ray-CT
Effects of motion
and heterogeneities
in proton therapy
(from Su et al 2010)
Fig. 2d. 3D views of dose distributions recorded in
gels by static (left) and motion (right) deliveries,
showing the 60% (light) and 90% (dark) isodose
surfaces.
Fig. 2. b. Orthogonal views of measured (OCTOPUSIQ data) dose distributions for static (left column) and
motion (right column) deliveries. The contour lines
indicate 60% and 90% isodose lines for measured
(dashed) and expected (solid) distributions.
Courtesy of MGS Research
Jirasek, Hilts et al, IC3DDose2010
CT polymer gel dosimetry: detection
of set-up error in H&N IMRT
•
CT polymer gel dosimetry: detection
of set-up error in H&N IMRT
•
Clear indication of treatment localization error in measured 3D
dose distribution
IMRT irradiation with and without known set-up error
Head and neck phantom
for 3D CT gel dosimetry
Planned treatment position
Planned
set-up
Isodose Overlay
Dose Difference
Localization error
Gamma (3%,3mm)
Set-up
error
Sup/Ant/Rt view
Measured and calculated doses for the IMRT plan irradiated with and
without a known set-up error: 3mm Lt, 4mm Post and 5mm Sup.
Sup/Post/Lt view
Sup/Ant/Rt view
Sup/Post/Lt view
The 90% isodose surface is rendered: planned (red); measured (green).
M Hilts 2011 | 21
0.15
20 MeV Electron Beam
15 MV Photon Beam
12 MeV Electron Beam
6 MeV Electron Beam
6 MV Photon Beam
Gulmay 80 kVp
Cobalt-60 (cuvettes)
0.15
-1
0.05
Dose (Gy)
0.1
Wellhofer
Optical CT
2
Δ μ (cm )
-1
• Radiochromic (dark)
– Optical contrast is absorbing
– Broad-beam fast scanning
Dose-to-Attenuation Calibration
Δμ (cm )
Radiochromic gels
Fricke (xylenol orange)
M Hilts 2011 | 22
100 M u/min
400 M u/min
0.1
15 MV
6 MeV
12 MeV
1
0.05
20 MeV
0
• Non-toxic, no oxygen sensitivity,
easy to make, energy independent
6 MV
0
1
2
80 kVp
Dose (Gy)
0
0
0
1
Dose (Gy)
2
0
5
Depth (cm)
10
• Diffusion, temperature (0.1deg),
light scatter, auto-oxidation
Olding and Schreiner, IC3DDose 2010
4
Head-and-Neck IMRT Treatment Plan
Wax Rando with FXG gel dosimeter insert
Electron Beam
Calibration
Calibration &
Measurement Jars
Olding and Schreiner, IC3DDose 2010
Olding and Schreiner, IC3DDose 2010
VISTATM Scanner*
IMRT Delivery
Dosimetric Evaluation*
Eclipse Plan
Gel Measurement
Using the 590 nm amber LED diffuse light source
Projection data acquired with a 1024x768 pixel, 12-bit CCD
camera using a 2/3” diameter, 12 mm focal length lens
Olding and Schreiner, IC3DDose 2010
*Modus Medical Devices Inc, London, ON, Canada
IMRT Delivery Evaluation
*in the CERR environment in MATLAB
Radiochromic Plastic:
Presage
• Accurate:
• Tissue equivalent
• Economical
3%, 3mm gamma test
max = 633 nm
5 Beam Tx
5
Benchmarking DLOS/Presage
DLOS : Duke Large Field-of-View Optical-CT Scanner
A.
Design Specifications
minutes
LED,
diffuser
filter
10 cm
16 cm
Dosimeter
8 Gy
0.175 mm
10
4 Gy
cm
6x6cm2
scan time
Dose Plateaus
C.
12 Gy
24
voxel size
PDD Top
16 cm
Aquarium
CCD
D.
4 Field Box
10 cm
F.
Linear Output
80 Gy
20 Gy
4x4cm2
4Gy
E.
Small Field
Output Factors
4 cm
40 Gy
FOV
B.
PDD Side
10 Gy
10 cm
3 cm
16 cm
Benchmark Data Set #4 4 field box
Benchmark Results:
Treatments delivered to Presage in RPC phantom
Benchmarking done
•
•
•
•
2mm resolution 15 mins
Accurate within 2% relative
Noise within 2%
Time within 30 mins after irradiation
First clinical application:
6 base-of-skull IMRT,
delivered to Presage in RPC H&N credentialing
phantom
#1
#2
#3
#4
#5
#6
6
Summary
Case 1
Plan
PTV
cm3
HN1
4.28
HN2
29.42
HN3
1.98
HN4
46.18
HN5
9.36
HN6
7.61
Portal Dosimetry
(3%, 3mm),
Mean (Range)
99.7%,
(99.2 – 99.9)
98.8%
(97.9 – 99.7)
99.5%
(99.2 – 99.7)
99.4%
(98.9 – 99.8)
98.9%
(97.9 – 99.4)
97.3%
(96.3 – 97.9)
DLOS/Presage
(3%, 3mm)
98.5
98.1
99.7
91.2
98.7
Patient Plan
95.7
Best Case 4
Transverse
99.4%
Saggittal
Coronal
Eclipse
Presage
Isodose
Measured
Case #1: illustrative comparisons
NDD Pass Rate
= 97.6%
Calculated
NDD Map
Measured
Transverse
Saggittal
Coronal
A clinical presentation of QA data ?
Worst
Case6
95.2%
DoseVolume Histograms
Phantom -> Patient
7
Can now compare measured and planned DVH
Eclipse Dose Map
98% pass Gamma Map
(3%, 3mm, 5% threshold)
50
1
Eclipse
Measurement
Patient
DVH etc
0
Phantom
-1
Medula Oblongata
PTV
Brainstem
3D Gamma
or NDD
Case 2 DVH in patient
Does 2D QA correlate with 3D ?
Presage
Eclipse
Conclusions
• 3D dosimetry now feasible
– Accurate, efficient, comprehensive, low cost
– commercialization ?
• Role of 3D
– Commissioning
– Routine QA ?
– Remote credentialing ?
• Expect clinically meaningful QA
Advanced Tx requires advanced verification !
www.IC3DDose.org
Academic Sponsors:
AAPM
SEAAPM
Duke Med. Phys. Graduate Program
Duke University Medical Center
Scientific Organizing Committee:
Sven Back (Sweden),
Clive Baldock (Australia),
Cheng-Shie Wuu (USA),
Yves De Deene (Belgium),
Simon Doran (UK),
Geoffrey Ibbott (USA),
Andrew Jirasek (Canada),
Kevin Jordan (Canada),
Martin Lepage (Canada),
Thomas Maris (Greece),
Mark Oldham (USA - Chair),
Evangelos Pappas (Greece),
John Schreiner (Canada)
8
Acknowledgments
Duke
• Andy Thomas
• Joe Newton
• Harshad Sakhalkar
• Pengyi Guo
• FangFang Yin
RPC
• Geoff Ibbott
• Ryan Grant
• Andrea Molineau
• Dave Followhil
Rider University
• John Adamovics (Presage)
Memorial SK
• Joe Deasy (CERR)
9
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
The Netherlands Cancer Institute
Antoni van Leeuwenhoek Hospital
2D analysis: e.g., multiple IMRT fields
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
Ben Mijnheer
3D analysis: e.g., VMAT verification
How should we verify complex radiation therapy
treatments ?
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
Ex-vivo: using phantom measurements
In-vivo: patient treatment verification
EPID dosimetry:
technical solutions
•
Advanced radiotherapy is a very complex process in which many variables are
influencing the intended dose delivery
•
Testing each sub-component in the patient treatment pathway is becoming virtually
impossible
•
Many persons are involved in the QA of the different steps thus introducing a risk
that the overall QA process has not been adequately covered
•
It is therefore necessary to have an “end-to-end” test to check the performance of
the total treatment chain
•
Such a test should evaluate the complete process from image-based treatment
design to dose delivery, and should preferably be performed by the same
persons who treat patients
•
For this purpose EPID dosimetry might play an important role
EPID dosimetry:
dose reconstruction models
Fluoroscopic screen /
video camera
Liquid-filled ionization
chamber
matrix
Amorphous
silicon (a-Si)
(van Elmpt et al., A literature review
of electronic portal imaging for
radiotherapy dosimetry, Radiother
Oncol, 88, 289-309, 2008)
(van Elmpt et al., A literature review
of electronic portal imaging for
radiotherapy dosimetry, Radiother
Oncol, 88, 289-309, 2008)
EPID dosimetry:
dose reconstruction models
EPID dose verification: 2D and 3D
Back-projection algorithm
Primary fluence prediction:
1) calculate
plan
- no straightforward correlation with dose
delivery in phantom or patient
- no end-to-end test
- no possibility for in vivo dosimetry
2) measure EPID dose
3) reconstruct dose in single or
multiple planes
(with/without patient or phantom
at NKI-AVL)
Back-projection of transit fluence:
- direct comparison with dose
delivery in phantom or patient
- end-to-end test (can be performed by
therapists)
- allows in vivo dosimetry
patient
or phantom CT
4) compare plan and reconstructed patient dose
(preferably at actual gantry angle)
Workflow of in vivo IMRT and
VMAT EPID dose verification
Gamma analysis of single IMRT fields
• EPID measurements at the linacs are
performed routinely by the therapists
• The analysis of the measurements is done by
two specialised (0.6 fte) therapists
(Kruse, Med Phys 37, 2516-2524, 2010)
(Nelms et al., Med Phys 38, 1037-1044, 2011)
Lack of correlation between gamma passing rates and clinically
relevant dose differences during single IMRT field verification,
particularly with highly modulated fields
2D EPID dose verification: IMRT
Patient record of γ-evaluation at NKI-AVL
Per field:
• mean γ
• max γ (1%)
• % points γ<1
• (isoc dose)
• Generally the first three fractions are verified
and an “average” of the three
measurements is used for pass/failure
analysis
•
A clinical physicist is warned by the therapists
in case of exceeding an action level
3D EPID dose verification: VMAT
For VMAT verification it was necessary to modify the
IMRT EPID dosimetry software:
• to incorporate gantry-angle resolved image acquisition
• to correct for EPID “flex” as a function of gantry angle
Per fraction
• isoc dose
Warning: yellow
Error: red
• to adapt the 3D back-projection model to include a
value for the transmission calculated from CT
data instead of using a measured value
• to reconstruct the total 3D dose distribution for
comparison with planned dose data using
a 3D gamma evaluation
3D EPID dose verification at NKI-AVL
3D EPID dose verification of a prostate VMAT
treatment
EPID movie
Dose per frame
Pinnacle3 (SmartArc module)
Elekta SL20i (standard 1 cm MLC)
Elekta iViewGT a-Si EPID
Treatment planning:
Delivery:
Verification:
Accumulated dose
(3 %, 3 mm)
γ
2
1
Single arc
In vivo verification / 10 MV beam / 80 s delivery time
-140°
0
50%
isodose
3D EPID dose distribution
140°
3D γ-evaluation
2D EPID dose verification: gamma analysis of
single IMRT fields
In vivo EPID dose verification results of the
first 45 VMAT prostate treatments
Action levels error
warning
ok applied at NKI-AVL
∆Disoc = 0.2 ± 1.6%
EPID dose verification: 2D vs 3D
EPID dose verification: 2D vs 3D
5-field IMRT rectum treatment
5-field IMRT rectum treatment
γ
γ
0
2D result (per beam), γ 3%/3mm, 20% isodose line
1
2
0
3D result (total dose), γ 3%/3mm, 50% isodose surface
2
3D result for γ evaluation within various isodose surfaces
γ
Isodose
2.0%/2.0mm
Same planes through 3D-γ-volume
1
2D result (per beam), γ 3%/3mm, 20% isodose line
2.0%/3.0mm
3.0%/3.0mm
90%
80%
70%
60%
50%
40%
30%
20%
EPID dose verification: summary of 3D VMAT QA
EPID dose verification: 2D vs 3D
5-field IMRT rectum treatment
No simple transition of evalution criteria from 2D to 3D !
Site
Prostate
Lung
3D result for γ evaluation within various isodose surfaces
Isodose
γ
90%
80%
70%
60%
50%
40%
30%
Brain
EPID (in vivo)
Dose diff (%)
EPID (in vivo)
% γ<1
Octavius (phantom)
% γ<1
-0.5 ± 2.2
95.0 ± 7.0
99.1 ± 1.0
129 pat.
129 pat.
5 pat.
-0.1 ± 3.5
94.1 ± 7.7
98.1 ± 3.0
49 pat.
49 pat.
5 pat.
-3.5 ± 3.1
90.0 ± 9.5
97.6 ± 1.7
32 pat.
32 pat.
7 pat.
20%
2.0%/2.0mm
Very satisfactory VMAT QA results
2.0%/3.0mm
3.0%/3.0mm
Head-and-neck cancer: 3D VMAT QA
EPID dose verification: 3D VMAT QA
EPID dosimetry
(phantom)
dose
gamma (3%, 3mm)
Pass rate
= 81%
Octavius
(phantom)
Prostate, lung, brain:
Head-and-neck:
• small spherical target volumes
•
•
•
Hypopharynx cancer: 3D VMAT QA
•
Hypopharynx cancer: 3D VMAT QA
Treatment planning: modified technique
- somewhat larger segments (11% increase in area)
•
large irregular target volumes
irregular (narrow) segments
highly modulated dose rate
Octavius: re-calibration
•
EPID dosimetry: EPIDs individually calibrated
- calculated transmission slightly different for each EPID
- actual dose values were 1.5% below calibration
arc 1
(98.7 % pass rate)
arc 2
EPID dose verification: 2D and 3D
• Extensive pre-treatment verification is
necessary during the commissioning process of
new equipment, and before the implementation of a
new treatment technique for a specific treatment
site
• By combining the information from 3D phantom
measurements using EPID dosimetry and other
detector systems, systematic errors observed in
both approaches can be traced and improved
EPID dose verification: ex-vivo and in-vivo
•
Ex vivo stands for: “in an artificial environment outside the
living organism”
•
In radiation dosimetry this means the measurement of dose
before or after a patient treatment using a phantom to
represent the patient
•
An ideal phantom configuration should have the same
external and internal dimensions, the same composition or
electron density, as well as the same setup as used during
the actual patient treatment (positioning/ fixation devices)
EPID dose verification: ex-vivo and in-vivo
EPID dose verification: ex-vivo and in-vivo
•
In vivo: Latin for “within the living” and indicates the use of a
whole, living organism
•
In radiation dosimetry this means the measurement of dose
received by the patient during treatment
•
In vivo does not imply that the detector is placed “within the
living”
•
In vivo dosimetry provides information that cannot be
obtained from ex vivo measurements
Many phantom-detector combinations are available for end-to-end tests
Rectum IMRT: change in patient anatomy
Breast IMRT: influence of contour change on dose distribution
Swollen breast tissue
EPID dosimetry confirms accurate dose delivery to breast
23.8 cm
CT #1, sagittal slice
17.9 cm
CT #2, sagittal slice
patient thickness changed: re-planned
Head-and-neck IMRT: change of internal anatomy
Head-and-neck IMRT: change of internal anatomy
Green: cone-beam CT scan; purple: planning CT scan with filled air cavity
Breast non-IMRT fields: incorrect positioning of jaws
Breast non-IMRT fields: incorrect positioning of jaws
incorrect beam
correct beam
Checkbox accidentally unchecked in a new version of Mosaiq
Result: 5.1 Gy underdosage in 1 beam for 6 fractions (out of 28)
Total dose: 50.7 Gy (deviation 10%)
Compensation: extra beam for remaining fractions
Lung: recovery from atelectasis;
incorporation of cone-beam CT
Is there a need for in vivo EPID dose verification?
YES!
(Anton Mans et al., Med Phys 37, 2638-2644, 2010)
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
Future developments for large scale implementation of EPID
Conclusions-1
dose verification:
•
•
•
•
•
availability of dedicated commercial solutions
fast dose reconstruction and analysis (NKI-AVL: IMRT within 1 min; VMAT
within 2-3 min)
simple user-friendly analysis software which can be handled by therapists
(e.g., only patient ID input and start analysis)
drafting clinical guidelines for action levels in 2D and 3D
combination with setup verification (e.g., cone-beam CT)
EPID dose verification:
2D and 3D, ex-vivo and in-vivo
Conclusions-2
• EPID in vivo dose verification provides a safety net for complex
treatment techniques such as IMRT and VMAT, as well as a full
account of the dose delivered to a patient
linac QA
• EPID dosimetry in combination with other detectors and phantoms is a
very useful approach for the verification of new treatment techniques
• EPID dosimetry is fast and accurate and provides comprehensive
information about the 3D dose distribution delivered to phantoms or
patients
• EPID in vivo dosimetry can serve as a substitute for patient-specific pretreatment verification using phantoms, yielding information about the
actual patient treatment
Many thanks to my colleagues at NKI-AVL:
Anton Mans
Hanno Spreeuw
Leah McDermott
Joep Stroom
Igor Olaciregui-Ruiz
Rene Tielenburg
Thijs Perik
Marcel van Herk
Roel Roozendaal
Ron Vijlbrief
Jan-Jakob Sonke
Markus Wendling
TPS QA
pre-treatment QA
IGRT
in vivo EPID dosimetry
for borrowing their slides and useful discussions!