RapidArc: Clinical Implementation

Transcription

1 RapidArc: Clinical Implementation Fang-Fang Yin, PhD Q. Jackie Wu, PhD Acknowledgements Team efforts from staff at Duke Radiation Oncology, especially to Dr. J Chang, Dr. J O Daniel for providing slide information Technical and financial supports from Varian Medical Systems Duke University Medical Center Clinical Implementation of VMAT Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance Fundamentals for VMAT Intensity Modulated arc therapy (VMAT) An arc-based approach to IMRT To be delivered on a conventional linear accelerator with a conventional MLC During an arc, the leaves of the MLC move and dose rate changes continuously as the gantry rotates RapidArc is one format of VMAT 1

2 The Principle of IMRT: Dose Painting Conventional 3-field RT Expected 3-field IMRT Static and Rotational IMRT Static gantry IMRT VMAT Typical dose distribution OAR PTV Beam Profile OAR PTV Multiple apertures At each angle One aperture At each angle The Format of Cone-Beam IMRT Static Gantry IMRT Rotational IMRT Volumetric Rotational IMRT Options Existing Planning Systems Eclipse (Varian) Duke choice ERGO++/Monaco (Elekta) Pinnacle SmartArc (Philips) Prowess (Prowess) o One of 7 fields One arc from 179 o 181 o Count-clockwise Existing Delivery Systems RapidArc (Varian) Duke choice VMAT (Elekta) Cone-beam Therapy (Siemens) (WIP) Existing QA Systems Matrixx Duke choice for routine QA Film Duke choice for commission SunNuclear Delta 4 Duke choice for future QA device Optical Scanner 2

3 Where Are We (Duke)? Started investigation in June 2008 A research RapidArc planning station from Varian Clinical installation in October Acceptance testing, commissioning, QA programs Single arc, no couch rotation, partial arc First patient treatment December 2008 New versions in August 2009 and May 2011 Allow multiple arcs, couch rotation, partial blocking, etc. Clinical Implementation of RapidArc Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance Infrastructure/Installation Staff (dedicated and trained) Existing machines: 21EX machine with 120-leaf millennium MLC NovalisTx with 120-leaf HD MLC (SRS, SRT,SBRT) ARIA version 8.6 or above (v10 now) Eclipse planning station (hardware and software) QA equipment Clinical Implementation of RapidArc Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance 3

4 Acceptance Testing Machine readiness Verification of installation against items included in the purchase order Inspections of safety and quality of installation and components VMAT performance Testing of functionality of each component and system performance against specifications. End-to-end testing Dry-runs for a few test case from simulation to delivery Acceptance Testing Sample Test 1.1: Gantry Angle Calibration Tolerance: Test 1.2: Isocenter Calibration Tolerance: + 1 mm Test 1.3: General Arc Dosimetry Range: 0.2 MU/ to 5.0 MU/ Tolerance: + 1% Acceptance Testing Sample Test 1.4 dmlc Dosimetry 0.5cm MLC slit sliding over 4 cm range Gantry: 0, 90, 270, 180 Acceptance Testing Sample Test 2.1: Accuracy of dmlc position vs. gantry position Tolerance: + 1 mm Tolerance: + 2% (over mean value) 4

5 Acceptance Testing Sample Acceptance Testing Sample Test 2.2: Accuracy of dmlc position during arc Tolerance: + 1 mm 2.1: Picket Fence vs. Gantry Angle (static) Acceptance Testing Sample Acceptance Testing Sample 2.1: Picket Fence vs. Gantry Angle (static) 5

6 Acceptance Testing Sample Acceptance Testing Sample Test 2.3: Ability to accurately detect MLC position error Criteria: detect submillimeter error in position 2.3: Picket Fence with Errors Acceptance Testing Sample Test 2.4: Accuracy of dose rate and gantry speed control during RapidArc Tolerance: + 2% Acceptance Testing Sample Test 2.5: Ability to control leaf speed/position during RapidArc Tolerance: + 2% 6

7 Relative Dose Percent Deviation (%) Acceptance Testing Sample Off y-axis : -100 mm Off y-axis : 0 mm Off y-axis : 100 mm Gantry speed vs Dose rate 1.02 (Tolerance 2%) Off x-axis Position (mm) Acceptance Testing Sample Off y-axis: -100 mm Off y-axis: 0 mm Off y-axis: 100 mm Variation of gantry speed and dose rate (tolerance 2%) Off X-axis Position (mm) Commissioning Validate that VMAT is capable of delivering radiation beams as good as SG-IMRT could Define the limitations of planning optimization, gantry rotation, beam blocking, couch rotation, and leaf speed, collimator settings Develop treatment process and documentation Workflow for RapidArc Treatment Case selection Immobilization/simulation Planning/prescription Quality assurance Target localization Treatment/validation 7

8 Clinical Implementation of RapidArc Planning - Process Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance SG-IMRT RapidArc Planning - Preparation Site-specific, for each site 10 cases from previous IMRT Develop RapidArc plan with different options Comparison between IMRT vs. RapidArc Constraint/optimization Optimization algorithm Constraints sensitivity Planning - Strategy Selected site-specific planning strategy 1 arc: prostate only, prostate bed, prostate+sv, brain lesions 2 arcs: prostate+sv+ln, spinal, brain lesions Multiple arcs: Head and neck, brain lesions, analrectal Partial arcs: partial breast, liver, 8

9 Planning - Optimization Key challenge interconnectivity of the beam shapes within consecutive VMAT gantry positions Constraints Target and normal structures Mechanicals Optimization algorithms More parameters Aperture based objectives and algorithms Planning Quality and Efficiency MLC segments Number of segments: IMRT RapidArc Plan quality is comparable if same segments More segments: slow gantry rotation for RapidArc More segments: long treatment time Planner experience Understand algorithm Understand limitations Planning - Logistics Training multiple people involved in the planning Gaining experience Develop planning protocols Last ~ 3 months before patients start Clinical Implementation of RapidArc Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance 9

10 Delivery - Tolerances Delivery Sample Parameters MLC leaf motion Leaf motion limit: 2.5 cm/s, 5 mm/degree Dose rate and gantry rotation speed One arc = one field MU, doserate, gantry speed linked Larger MU max doserate varying gantry speed Smaller MU max gantry speed varying doserate Middle varying gantry speed and doserate RapidArc Delivery Limits Variable gantry speed degree/sec Variable dose rate MU/min ( Novalis Tx) Variable dose per degree MU/degree Variable MLC speed cm/s Delivery - Efficiency Plan quality The quality of plan number of apertures Single arc 177 apertures Complexity structures: more apertures/arcs multiple arcs Delivery time Single arc less time (< 2 mins) but sometimes inferior quality Multiple arcs better quality but longer time 10

11 Delivery Treatment Time Treatment time = Patient set-up time + Delivery time Delivery time=beam-on time+between beam=on time Patient setup time: no reduction Beam-on time: 20-60% reduction (less MUs) Between beam-on time: 100% saving for single arc 20-60% saving for multiple arcs Delivery Partial Arc Mechanical collision If isocenter is close to center full arc If isocenter is close to peripheral partial arc Partial blocking is also available Partial RapidArc for Liver SBRT Multiple Arcs vs. Single Arc Single arc RapidArc MU = 714 IMRT Total MU = 1572 Multiple arcs Time: 1.3 min 11

12 VMAT For Large Size PTV VMAT For Large PTV Large field size -> sometimes IMRT beam has triple beam splits Multi-sections (parts) of the PTV, large variation of PTV shape, OARs and their constraints 3 Arcs, 1000 degree rotation 17cm Field Size << PTV in some directions Beam orientation selection is part of IMRT planning, is often not used for RapidArc (i.e. full arc) VMAT For Large Size PTV VMAT For Large PTV IMRT VMAT17cm IMRT VMAT17cm 12

13 D1% (%) VMAT For Large PTV IMRT VMAT17cm VMAT For Large PTV VMAT26CM VMAT 17cm VMAT For Large PTV Field Size Effect On VMAT Planning Quality VMAT17cm VMAT23cm 160 PTV Hot Spot (D1%) 150 Collimator 30 Collimator Projected Field Size X (cm) 13

14 VMAT For Head-and-Neck VMAT For Head-and-Neck VMAT IMRT Field Thru Shoulder Field Thru Shoulder VMAT For Head-and-Neck RapidArc For Head-and-Neck VMAT IMRT Rt Parotid Oral Cavity Cord Lt Parotid Pharynx 14

15 VMAT For Head-and-Neck Clinical Implementation of RapidArc Segments Thru Shoulder Fundamentals for RapidArc Infrastructure/Installation Acceptance testing/commissioning Planning Delivery Quality assurance Quality Assurance Quality Assurance The QA program for the VMAT is similar to SG-IMRT in principle but with different measurement approaches due to its dynamic nature that, during VMAT delivery, MLC leaves are moving Gantry is rotating Dose rate is changing The QA program: validate the functionality and performance of accepted features For each planned delivery Patient specific QA Machine specific QA 15

16 Quality Assurance Machine specific QA accuracy of the MLC leaf positions during VMAT delivery ability of the system to accurately vary the dose rate and gantry speed during VMAT delivery ability of the system to accurately vary the MLC leaf speed during VMAT delivery Tolerances: Acceptance baselines Machine QA Chart Daily Standard linac QA Standard MLC QA Rotational delivery of dose to an ion chamber phantom Monthly Leaf motion Gantry rotation Dose output leaf motion gantry motion dose rate changes Patient Specific QA Hybrid QA technique Plan to phantom Dose measurement to phantom Rotational nature Not to single plan Phantoms Instruments Ion chamber 2-D array (ion chamber, diodes, film, ) Patient Specific QA Data analysis Multiple planes (axial, coronal, sagittal) Profiles Points Gamma analysis Collision check Before patient on the couch When patient on the couch 16

17 RapidArc QA vs. IMRT QA More complex treatment delivery Varying gantry angle, gantry speed, dose rate, and MLC leaf motion ImSure does not calculate dose for RapidArc delivery Current IMRT technique: Portal dosimetry RapidArc technique: Ion chamber, film, and Matrixx QA Measurements Ion chamber Absolute dose: (meas calc) / calc < 3% Film (coronal, sagittal, and axial planes) Optional Matrixx (coronal and sagittal planes) 3-6 hrs/patient Gold Standard QA Tools Ion Chamber Film Ion Chamber Equipment 0.13cc or 0.01cc ion chamber Calibration 10x10cm 2, 100SSD, depth = d max, 200MU cgy/nc correction factor RA delivery Center of 30cm x 30cm x 20cm solid water phantom Compare to Eclipse calculation 39 VMAT plans 17

18 Film Equipment Kodak EDR2 film OmniPro ImRT Calibration 12 2cm x 2cm squares 0 300cGy RA delivery MultiCube (IBA dosimetry) Coronal, sagittal, and axial planes Compare to Eclipse calculation Gamma analysis 8 MAT plans Verification with Gold Standard QA Ion chamber: Median: +1.7% Range: -0.9% - 2.8% Film 24/24 > 93% passing rate 23/24 > 95% passing rate 20/24 > 97% passing rate Ion Chamber vs. Eclipse Result: Axial Film vs. Eclipse Ion chamber array vs. Eclipse Eclipse 3%, 3mm DTA, 5% threshold Film 18

19 Front Back % Pixels Passing Gamma (<1) % Pixels Passing Gamma (<1) 100 Film vs. Film vs. Eclipse 100 Film Film vs. Eclipse %, 3mm DTA, 5% threshold Plan # Coronal Sagittal Axial %, 3mm DTA, 5% threshold Sagittal and Coronal, 40% threshold Axial 3%, 3mm, axial thresholds up to 40% Plan # Coronal Sagittal Axial Validation of 2D Ion Chamber Array Angular Dependency: MatriXX Evolution (IBA Dosimetry) 1020 ionization chambers 0.07 cm 3 sensitive volume 0.4cm diameter 24 x 24 cm 2 grid 7.6mm spacing Automatic temperaturepressure correction Future solution from IBA: Gantry angle sensor Apply correction factor to each ion chamber based on angularity +2.2% 15x +3.0% 6x Measured/Calculated (%) +2.0% 15x +2.8% 6x -1.8% 15x -3.5% 6x Herzen et al., PMB 2007; 52: % 15x -1.7% 15x +3.7% 6x -2.0% 6x 19

20 %Difference from Eclipse Calculation %Pixels Passing Gamma (<1) %Pixels Passing (Gamma <= 1) Matrixx QA Results Patient Specific QA 100 Matrixx vs Eclipse MatrixxCoronal 3%, 3mm, axial thresholds up to 5% MatrixxSagittal RapidArc (Plan #) Ion Chamber Fig. vs. 1: Ion Eclipse Chamber vs. Eclipse & and ICA Matrixx vs. Eclipse Eclipse 6% IC IC Array 4% Film vs. Ion Film vs. Chamber Ion Array Array 2% 96 0% -2% % -6% Brain Prostate Bed Plan # Prostate Prostate + SV Spine 90 Coronal Sagittal Gamma = 3%, 3mm, 5% threshold Plan # 20

21 Effective vs. Efficient Stage 1: Intensive QA Ion chamber, film in 3 planes, ion chamber array in 2 planes, 3D polymer gel dosimetry Stage 2: Rigorous QA Ion chamber, ion chamber array in 2 planes Stage 3: Effective and Efficient QA Ion chamber, ion chamber array in 1 plane Ion chamber array only Effective vs. Efficient Preparation Delivery Analysis Ion chamber 1 st Film 1 st Ion chamber array 1 st Ion chamber additional Film additional Ion chamber array additional IC + 3 Film + 2 ICA IC + 2 ICA IC + ICA Effective vs. Efficient When implementing a new technology Perform intensive patient-specific QA for the first group of patients Rely on QA gold standards 3D QA very useful Use gold standard QA technology to transition to newer QA devices Goal: Effective QA Conclusion RapidArc is one format of rotational IMRT for dose painting Implementation of RapidArc requires careful planning, testing, and verifications. Thoroughly testing and commissioning are necessary prior to patient treatment QA is a critical step, always compare with static field IMRT plan in the early phase RapidArc should be judged by its accuracy, safety, efficiency, applicability, integration, and adaptation 21

22 Thank you for your attention 22