How Should We Verify Complex Radiation Therapy Treatments?

Transcription

1 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. How should we verify complex radiation therapy treatments? Comprehensive verification: the role of 3D Dosimetry. Rationale for 3D? catch more errors 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 Gradient Further rationale - 2D QA does not correlate with 3D 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

2 Partial Review of 3D dosimetry systems? Material Polymer gels Radiochromic gels FX-orange Radiochromic plastics Presage Read-out MRI X-ray-CT 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? Wuu et al., IC3DDose2010 Baldock et al. 55 (5) Phys Med Biol Optimizing the multiple spin echo sequence RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY Image artifacts: Temperature drift RESEARCH GROUP QUANTITATIVE MRI IN MEDICINE AND BIOLOGY S NOT OPTIMAL S OPTIMAL S i T 2 TE T 2 TE TE 1 TE 2 TE 3 TE 4 T 2 R 2 R GEL DOSIMETER: CORONAL reconstructed from TRANSVERSE slices GEL DOSIMETER: CORONAL (scanned) TPS: Pinnacle R 2 map R 2 [s -1 ] Dose map D TPS: TRA GEL: TRA Dose [Gy] Calibration plot SSE requires 24 acquisitions to obtain the same SNR as a MSE with 32 echoes!! TPS: SAG GEL: SAG Yves DeDeene: IC3DDose 2010 Yves DeDeene: IC3DDose

3 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 Brachytherapy dosimetry using BANG gel and a 100 um pixel laser scanner (at NIST) Wuu et al, IC3DDose2010 Courtesy of MGS Research Brachytherapy measurements (from Massillon et al PMB 2009) 230 MeV Protons: BANG vs Ion Chamber (from Zeidan et al 2010) Courtesy of MGS Research Courtesy of MGS Research 3

4 Effects of motion and heterogeneities in proton therapy (from Su et al 2010) X-ray-CT Fig. 2. b. Orthogonal views of measured (OCTOPUS- IQ 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. 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. Courtesy of MGS Research Jirasek, Hilts et al, IC3DDose2010 CT polymer gel dosimetry: detection of set-up error in H&N IMRT IMRT irradiation with and without known set-up error CT polymer gel dosimetry: detection of set-up error in H&N IMRT Clear indication of treatment localization error in measured 3D dose distribution Head and neck phantom for 3D CT gel dosimetry Planned set-up Planned treatment position Localization error Isodose Overlay Dose Difference Gamma (3%,3mm) Set-up error Sup/Ant/Rt view Sup/Post/Lt view Sup/Ant/Rt view Sup/Post/Lt 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. The 90% isodose surface is rendered: planned (red); measured (green). M Hilts M Hilts Radiochromic gels Fricke (xylenol orange) Dose-to-Attenuation Calibration Radiochromic (dark) Optical contrast is absorbing Broad-beam fast scanning Non-toxic, no oxygen sensitivity, easy to make, energy independent Diffusion, temperature (0.1deg), light scatter, auto-oxidation Δμ (cm -1 ) 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) Dose (Gy) Δμ (cm -1 ) M u/min 400 M u/min Dose (Gy) Dose (Gy) MeV 12 MeV 80 kvp Depth (cm) Wellhofer Optical CT 6 MV 15 MV 20 MeV Olding and Schreiner, IC3DDose

5 Head-and-Neck IMRT Treatment Plan Wax Rando with FXG gel dosimeter insert Electron Beam Calibration IMRT Delivery Calibration & Measurement Jars Olding and Schreiner, IC3DDose 2010 Olding and Schreiner, IC3DDose 2010 VISTA TM Scanner * Dosimetric Evaluation* 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 *Modus Medical Devices Inc, London, ON, Canada Eclipse Plan Gel Measurement Olding and Schreiner, IC3DDose 2010 *in the CERR environment in MATLAB IMRT Delivery Evaluation Radiochromic Plastic: Presage Accurate: Tissue equivalent Economical 3%, 3mm gamma test max = 633 nm 5 Beam Tx 5

6 DLOS : Duke Large Field-of-View Optical-CT Scanner Design Specifications Benchmarking DLOS/Presage A. B. C. PDD Side PDD Top Dose Plateaus FOV 24 cm voxel size mm scan time 10 minutes LED, diffuser filter Dosimeter Aquarium CCD D. 16 cm 4 Field Box 6x6cm 2 E. 10 cm Small Field Output Factors 4 cm F. 4 Gy 12 Gy 8 Gy 16 cm Linear Output 80 Gy 4Gy 4x4cm 2 40 Gy 20 Gy 10 cm 3 cm 16 cm 10 Gy 10 cm Benchmark Results: Benchmark Data Set #4 4 field box Benchmarking done 2mm resolution 15 mins Accurate within 2% relative Noise within 2% Time within 30 mins after irradiation #1 Treatments delivered to Presage in RPC phantom #2 #3 First clinical application: 6 base-of-skull IMRT, delivered to Presage in RPC H&N credentialing phantom #4 #5 #6 6

7 Summary Case 1 Plan PTV cm3 Portal Dosimetry (3%, 3mm), Mean (Range) DLOS/Presage (3%, 3mm) HN HN HN HN HN HN %, ( ) 98.8% ( ) 99.5% ( ) 99.4% ( ) 98.9% ( ) 97.3% ( ) Patient Plan Case #1: illustrative comparisons Best Case % Transverse Saggittal Coronal Measured Eclipse Presage NDD Pass Rate = 97.6% Isodose Measured Calculated NDD Map Worst Case6 95.2% Transverse Saggittal Coronal A clinical presentation of QA data? DoseVolume Histograms Phantom -> Patient 7

8 Can now compare measured and planned DVH Eclipse Measurement 98% pass Gamma Map (3%, 3mm, 5% threshold) 1 Eclipse Dose Map 50 Patient DVH etc 0 Phantom 3D Gamma or NDD Medula Oblongata PTV Brainstem -1 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! 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

9 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

10 The Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital EPID dose verification: 2D and 3D, ex-vivo and in-vivo 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 EPID dose verification: 2D and 3D, ex-vivo and in-vivo How should we verify complex radiation therapy treatments? Advanced radiotherapy is a very complex process in which many variables are influencing the intended dose delivery Ex-vivo: using phantom measurements 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 In-vivo: patient treatment verification 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: technical solutions 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, , 2008) (van Elmpt et al., A literature review of electronic portal imaging for radiotherapy dosimetry, Radiother Oncol, 88, , 2008)

11 EPID dosimetry: dose reconstruction models EPID dose verification: 2D and 3D Back-projection algorithm Primary fluence prediction: - no straightforward correlation with dose delivery in phantom or patient - no end-to-end test - no possibility for in vivo dosimetry 1) calculate plan 2) measure EPID dose 3) reconstruct dose in single or (with/without patient or phantom multiple planes 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) Gamma analysis of single IMRT fields Workflow of in vivo IMRT and VMAT EPID dose verification (Kruse, Med Phys 37, , 2010) (Nelms et al., Med Phys 38, , 2011) 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 Generally the first three fractions are verified and an average of the three measurements is used for pass/failure analysis Lack of correlation between gamma passing rates and clinically relevant dose differences during single IMRT field verification, particularly with highly modulated fields A clinical physicist is warned by the therapists in case of exceeding an action level 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) Per fraction isoc dose Warning: yellow Error: red 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 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

12 3D EPID dose verification of a prostate VMAT treatment EPID movie Dose per frame Accumulated dose 3D EPID dose verification at NKI-AVL Treatment planning: Pinnacle 3 (SmartArc module) Delivery: Elekta SL20i (standard 1 cm MLC) Verification: Elekta iviewgt a-si EPID (3 %, 3 mm) γ 2 1 Single arc In vivo verification / 10 MV beam / 80 s delivery time 50% isodose 3D EPID dose distribution 3D γ-evaluation 0 In vivo EPID dose verification results of the first 45 VMAT prostate treatments 2D EPID dose verification: gamma analysis of single IMRT fields Action levels error warning ok applied at NKI-AVL D isoc = 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 2D result (per beam), γ 3%/3mm, 20% isodose line γ D result (per beam), γ 3%/3mm, 20% isodose line γ D result (total dose), γ 3%/3mm, 50% isodose surface 3D result for γ evaluation within various isodose surfaces Same planes through 3D-γ-volume γ Isodose 2.0%/2.0mm 2.0%/3.0mm 3.0%/3.0mm 90% 80% 70% 60% 50% 40% 30% 20%

13 EPID dose verification: 2D vs 3D EPID dose verification: summary of 3D VMAT QA 5-field IMRT rectum treatment No simple transition of evalution criteria from 2D to 3D! 3D result for γ evaluation within various isodose surfaces γ Isodose 90% 80% 70% 60% 50% 40% 30% 20% 2.0%/2.0mm 2.0%/3.0mm 3.0%/3.0mm Site Prostate Lung Brain EPID (in vivo) Dose diff (%) -0.5 ± pat ± pat ± pat. EPID (in vivo) % γ< ± pat ± pat ± pat. Very satisfactory VMAT QA results Octavius (phantom) % γ< ± pat ± pat ± pat. Head-and-neck cancer: 3D VMAT QA EPID dose verification: 3D VMAT QA EPID dosimetry (phantom) dose gamma (3%, 3mm) Octavius (phantom) Pass rate = 81% Prostate, lung, brain: small spherical target volumes Head-and-neck: large irregular target volumes irregular (narrow) segments highly modulated dose rate Hypopharynx cancer: 3D VMAT QA Hypopharynx cancer: 3D VMAT QA Treatment planning: modified technique - somewhat larger segments (11% increase in area) 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 arc 2 (98.7 % pass rate)

14 EPID dose verification: 2D and 3D EPID dose verification: ex-vivo and in-vivo 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 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 Many phantom-detector combinations are available for end-to-end tests In vivo dosimetry provides information that cannot be obtained from ex vivo measurements 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 17.9 cm CT #1, sagittal slice CT #2, sagittal slice patient thickness changed: re-planned

15 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, , 2010)

16 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 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) Conclusions-1 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 EPID dose verification: 2D and 3D, ex-vivo and in-vivo Many thanks to my colleagues at NKI-AVL: 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 TPS QA Anton Mans Leah McDermott Igor Olaciregui-Ruiz Thijs Perik Roel Roozendaal Jan-Jakob Sonke Hanno Spreeuw Joep Stroom Rene Tielenburg Marcel van Herk Ron Vijlbrief Markus Wendling pre-treatment QA IGRT in vivo EPID dosimetry for borrowing their slides and useful discussions!