Real-time and offline treatment delivery error detection via aSi EPID ...
Transcript of Real-time and offline treatment delivery error detection via aSi EPID ...
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Real-time and offline treatment
delivery error detection via aSi EPID
transmission dosimetry 1Jeffrey Siebers
1University of Virginia, Charlottesville, VA, USA
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Disclosures
• This work has been supported in part by 2013 ROI Grant from ASTRO "Safety and Quality:
IMRT treatment delivery accuracy“, Peter Greer PI
Varian Medical Systems (6/2015)
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Objectives
• Understand real-time EPID-based transmission dosimetry
goals of real-time delivery monitoring
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Background
• QA methods lag modern delivery capabilities
• Significant error pathways persist even when pre-treatment QA is performed R&V parameters could be altered inter-fractionally
unintentional modification while viewing, database corruption, …
Equipment could malfunction position encoder disconnect from leaf, …
Current pre-treatment QA is insensitive to delivery errors %γ<1 (3%,3mm) reliably detects 10% fluence errors in 20x20 mm2 area
During treatment motion & intra- & inter-fractional patient changes can occur
• Practical QA needed for real-time adaptive RT
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Planned
Delivery
EPID
Tx Delivery
EPID
Treatment QA Goal Approved Plan = Achieved in Patient
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during treatment uses
• dose back-projection-based estimators point-dose
iso-center-plane dose
3D-dose (PTV dose in accelerator coordinate system)
• tissue-localization ( ±fiducials)
• patient changes (Δ attenuation / tumor shrinkage)
• MLC leaf position variations
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Findings
• Gross error rates ~0.3%
• Most detected errors were not / would NOT
have been picked up by pre-treatment QA
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To date, EPID-base exit-fluence
has NOT been used to
27%
17%
10%
20%
27% 1. Monitor fiducial locations
2. Detect miss-positioned MLC leaves
3. Detect tumor spread
4. Re-compute PTV dose
5. Detect tumor response
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To date, EPID-base exit-fluence
has NOT been used to 1. Monitor fiducial locations:
Lin, W.-Y., et al. (2013). Real-time automatic fiducial marker tracking in
low contrast cine-MV images. Medical Physics, 40(1), 011715.
2. Detect miss-positioned MLC leaves: Fuangrod, T., et al. (2014). An independent system for real-time dynamic
multileaf collimation trajectory verification using EPID. Physics in Medicine
and Biology, 59(1), 61–81.
3. Detect tumor spread: This, to my knowledge, has not been reported in published works.
4. Re-compute PTV dose:
Mans, A, et al. (2010). Catching errors with in vivo EPID dosimetry.
Medical Physics, 37(6), 2638–2644.
5. Tumor shrinkage: McDermott, L. et al. (2006). Anatomy changes in radiotherapy detected
using portal imaging. Radiotherapy and Oncology, 79(2), 211–217.
http://doi.org/10.1016/j.radonc.2006.04.003
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To date, EPID-base exit-fluence
has NOT been used to 1. Monitor fiducial locations:
Lin, W.-Y., et al. (2013). Real-time automatic fiducial marker tracking in
low contrast cine-MV images. Medical Physics, 40(1), 011715.
2. Detect miss-positioned MLC leaves: Fuangrod, T., et al. (2014). An independent system for real-time dynamic
multileaf collimation trajectory verification using EPID. Physics in Medicine
and Biology, 59(1), 61–81.
3. Detect tumor spread: This, to my knowledge, has not been reported in published works.
4. Re-compute PTV dose:
Mans, A, et al. (2010). Catching errors with in vivo EPID dosimetry.
Medical Physics, 37(6), 2638–2644.
5. Tumor shrinkage: McDermott, L. et al. (2006). Anatomy changes in radiotherapy detected
using portal imaging. Radiotherapy and Oncology, 79(2), 211–217.
http://doi.org/10.1016/j.radonc.2006.04.003
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An example real-time QA program
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ASTRO Radiation Oncology Institute
Grant
• International consortium
• verification as the radiation is delivered to the patient for every fraction
• EPID-based detection
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Real-time verification
• diverse equipment
• goals: Implementation
Quantify gross error rate
Center Linac Energy MLC EPID
Calvary Mater Newcastle (CMN) – Lead Site C-Series (4) 6X Millenium aS1000
TB2.0 6X, 10X HDMLC aS1200
6XFFF, 10XFFF HDMLC aS1200
Northern Sydney Cancer Centre (NSCC) C-Series 6X Millenium aS1000
TB2.0 6X HDMLC aS1000
University of Virginia (UVA) TB1.5 6X, 10X, 15X Millenium aS1000
6XFFF, 10XFFF Millenium aS1000
C-Series 6X, 15X Millenium aS1000
Cancer Care of Virginia (CCM) C-Series 6X Millenium aS1000
Central Coast Cancer Center (CCCC) C-Series (2) 6X Millenium aS1000
Memorial Sloan Kettering Cancer Center (MSKCC) TB2.0 6X, 10X Millenium aS1000
TB2.0 6X Millenium aS1200
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• Predict using a model the “cine” EPID images that should be measured during the patient’s radiation delivery
• Acquire EPID cine images during the delivery (frame-rate ~ 7 Hz)
• Compare the measured to the predicted in real-time
Description of research project
Courtesy of Peter Greer
Detection within 0.14 sec
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Patient uncertainty
• Development of optimal error detection tools – patient uncertainties
Courtesy of Peter Greer
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WatchDog
Computer
Record and Verify Image Predictor (McCurdy)
Portal
Vision Frame
Grabber
D
I
C
O
M
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Prediction
Delivery
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>250 patients to date
Thousands of fractions
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Current WD application
• during-treatment-delivery Gross-error detection (>10% from Rx)
Active exit-fluence monitor
Active MLC-position monitoring
• post-treatment -delivery Non-gross error detection (>5%, <10%)
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EPID-base exit-fluence
dosimetry can detect gross
delivery errors as fast as
27%
17%
17%
23%
17% 1. Between patient fractions
2. Between beams of a fraction
3. Within 10 seconds
4. Within 1 second
5. Within < 0.2 seconds
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EPID-base exit-fluence
dosimetry can detect gross
delivery errors as fast as
5. Within <0.2 seconds
Fuangrod, T., et al. (2013). A system for EPID-based real-time
treatment delivery verification during dynamic IMRT treatment. Medical
Physics, 40(9), 091907.
Real-time gross error detection is currently
possible.
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UVA post-delivery tools
• Offline leaf position analysis Image-based edge
detection
Log-based
• Image-based larger deviation due to leaf motion during image acquisition
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UVA post-delivery tools
• Offline leaf position analysis Image-based edge
detection
Log-based
• Image-based larger deviation due to leaf motion during image acquisition
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UVA during-
treatment tools
• Beam monitoring
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• Beam monitoring Intentional error via
Tx beam miss-match
UVA during-
treatment tools
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Summary
• Described a delivery-system independent real-
time QA system
• Demonstrated functionality for gross error
detection
• May be possible to detect patient/attenuator
changes (in real time)
• Will enable on-line adaptive RT
permit quantification of inter-fractional error rates