Presentation on theme: "Workshop 2012 Serge Calippe - European Technical Support HW"— Presentation transcript:
1 Workshop 2012 Serge Calippe - European Technical Support HW RapidArc® Workshop 2012 January 27-28th 2012, Aarhus, Denmark
2 Session 1aRapidArc® – BasicsTechnical description of RapidArc® delivery on ClinacRapidArc® delivery of the TrueBeam® acceleratorDiscussionSession 1bOptimize RapidArc® delivery – Technical aspectWhy a specific Machine QC ?Hardware and software adjustments (MLC – Gantry – Beam performance)PMI / Machine QC (Tests, dynalog files)
3 Technical description of RapidArc® delivery on Clinac Session 1aRapidArc® – BasicsTechnical description of RapidArc® delivery on ClinacRapidArc® delivery of the TrueBeam® accelerator compared to Clinac)
5 RapidArc® – BasicsRapidArc® is a sophisticated treatment technique (….which started in Denmark in 2008)RapidArc® is a volumetric arc therapy that delivers a precisely sculpted 3D dose distribution with a single 360-degree rotation of the LinacSubstantially decreases the treatment time
6 RapidArc® – Basics Modulation of the dose distribution Varying doses per degree and dynamic MLC (DMLC)The variable dose per degree is achieved by changing both the dose rate or gantry speedMLC leaves are allowed to travel in and out + leaf Interdigitation capabilitiesThe arc optimization algorithm, PRO (Progressive Resolution Optimizer), ensures the treatment precision. It optimizes leaf position, dose rate and gantry speedDemo..\RapidArc_Treatment_Timing.mp4
7 Technical description of RapidArc® delivery on Clinac
8 Technical description RapidArc® on Clinac Operation and ControlFunctioning of the Clinac control system during RapidArc® deliverySynchronization of MLC, gantry and dose rateConstraints
9 Technical description RapidArc® on Clinac A full arc is divided in simple segments defined by control points.Parameters to control?Gantry angleDose delivered / dose rateMLC leaves positionsEach control point specifies the gantry angle, cumulative fractional MU and MLC positions
10 Technical description RapidArc® on Clinac Maximum 177 control points (at 5th level of Progressive Resolution Optimizer -PRO)1 segment every # 2 degrees for a full turn.For each single segment:Dose rate is constantGantry speed is constantStarting and ending of MLC leaves are knownGantry, MLC and MUs are monitored every 50msDose rate or gantry speed are adjusted if needed
11 RapidArc® – control points listing in Eclipse Cumulative MUGantry PositionDose RateGantry SpeedAn example of the RapidArc prescription as calculated and displayed by Eclipse. Each row represents control point.Note that the Dose Rate is kept at maximum whenever possible while gantry speed is varied. (see Index 59-68)Once the gantry maximum speed is reached (and that is a priority for the algorithm), the MU/degree variation is achieved by variations of the instantaneous dose rate. (see Index 69-79).The maximum gantry speed was limited in the algorithm to degrees/sec for this exapmle.
13 Technical description RapidArc® on Clinac The RapidArc® plan is moded up through the 4DITC, and is then divided in two groups of control parametersThe gantry angle as a function of cumulative MU is sent to the Clinac control system in the form of a segmented treatment table (STT)The MLC leaf positions as a function of gantry angle are sent to the MLC controller in the form of an arc dynamic beamThe treatment delivery is controlled by the Clinac controller and the MLC controller
14 Animation of variable dose delivered to individual segments This animation explains the concept of variable dose per segment, defined as gantry travel between the two control points. Intensity of the color corresponds with number of MU delivered in segment.The change in dose per segment can be achieved either by change of the dose rate or by change in gantry speed while keeping the dose rat constant.RapidArc delivery utilizes both methods hence substantially widening the modulation range compared with only one method.The dose per segment during the RapidArc delivery can vary between 0 MU/segment up to ~40 MU/segment for 360 degrees arc
15 RapidArc ® - Dose Rate & Gantry Speed Modulation Gantry Speed [deg/sec]Gantry Speed ModulationDose Rate ModulationRapidArc has instantaneous dose rate variation as shown by the blue line.Gantry speed variation extends the dynamic range when the dose rate is at its maximum.
16 RapidArc ® - Dose per Gantry Angle – MU/deg Gantry Speed ModulationDose Rate ModulationCorresponding MU/degree values from the previous slide.Gantry speed variation extends the dynamic range when the dose rate is at its maximum.
17 Technical description RapidArc® on Clinac Clinac controller maintains the relationship between MU versus Gantry positionMLC controller maintains the MLC versus Gantry position relationship
20 Technical description RapidArc® on Clinac MLC controller
21 Technical description RapidArc® on Clinac Gantry speed must slow down so that the MLC leaves can catch up to the specified leaf positionsMaximum treatment time depends on complexity of the treatment planGantry must slows down to deliver lots of doses or MUs or increase MU rateTo maximize treatment time, use lower prescribed dose or maximum MU rate
22 Technical description RapidArc® on Clinac J. Bocanek 07/2009Technical description RapidArc® on ClinacVariable gantry speed0.5 – 4.8 degree/secVariable dose rate0 – 600 MU/minVariable dose per degree0.2 – 20 MU/degreeVariable MLC speed0 – 2.5 cm/s (5 mm/degree)Note : It depends on energies / DRGantry speed values are stated for standard beams.SRS beam - iX machine – minimum gantry speed is 0.22 deg/secSRS beam – Trilogy – minimum gantry speed is 0.27 deg/secDose rate stated for standard beams.SRS beam – iX machine – maximum dose rate 800 MU/minSRS beam – Trilogy – maximum dose rate 1000 MU/minDose per degree stated for standard machineMaximum dose rate for SRS beam (iX and Trilogy) – 60 MU/degreeMaximum leaf speed limit used by the Eclipse for the optimization is 2.5 cm/s.
23 Technical description RapidArc® on Clinac Arcs / plan*Total arc / plan*Min arc*Segments may be avoidedMax dose : 7200 MU9999 MU for 6X SRS (7.9+)*Note : It depends on SW releases
24 During the treatment, the system can generate Logs: LOG FilesDuring the treatment, the system can generate Logs:Clinac console (Communication/Log): Generation of a Dynamic beam delivery Log4DITC WS : Generation of a MLC log (2 files Carriages A & B)
25 Dynamic MLC Arc log / Clinac Console OOPS!! January 2008!!!It is Not a RapidArc or VMAT Log!!!
27 MLC Log – Dynalog File Viewer Dynamic leaf deviationLog Activation :Because DynaLog files are typically large, Varian recommends that this feature should be turned OFF, and only activated when there is a specific need for DynaLog files to be saved.DiagAutoDynalogs 2,1 for SW 6.8DiagAutoDynalogs 1 for SW 7.xHow to read?
31 Control of the Dose rate Fast beam-on / beam-off control.On high energy Clinac : the key is the triode gridded gun(On Unique system : magnetron frequency)
32 Control of the Dose rate On high Energy Clinac the gridded electron gun allows Instantaneous dose rate controlThe cathode is heated to excite emissions of electrons. The injection is controlled by the grid.
35 Gridded GUN HE ClinacThe grid of the gun is used as an On/Off trigger which allows us to control the output electron emissions.A negative voltage is used to inhibit electron emissions and an approximately +160VDC pulse is used to allow the electrons to be released from the gun and into the guide.Gun is pulsed continuously for constant temperature and emissionThis gives us a very precise control so we can terminate or start the gun’s electron flow as required
37 Gridded GUN HE ClinacInjection pulses are coincident or delayed to RF pulses to produce beam pulses or not, based on the segments window.
38 Control of the Dose rate RapidArc®. Quality Assurance.J. Bocanek 07/2009
39 Gun controller KLY Current signal Used as the pulse Reference PULSE CONTROLGUN CONTROLLERKLY Current signalUsed as the pulse ReferenceConstant time relationship to RF power in the guide.
40 MLCThe MLC workstation integrated in the 4DITC, sends data for entire treatment for all leaves, including dose versus position information, to MLC Controller via serial linkMLC Controller will set MLC leaves in placeUpon start of treatment, MLC Controller sends commands to MLC head via optical link to move leavesMLC Controller compares planned and actual position of each leaf obtained from feedback system with the treatment plan
42 MLC - Primary Readout System Leaf Position is determined using 2 independent sourcesPrimary Readout utilizes encoder mechanically attached to motor’s shaft for both carriages and leafsCarriage540 counts = 1 mm of linear shift at isocenterLeaf707 counts = 1 mm linear shift for full width leafs512 counts = 1 mm linear shift for half width leafs at isocenter
43 MLC - Secondary Readout System / Interlock Secondary Feedback verifies, that motor count really represents actual motionCarriage – Mylar strip with fine black lines at the side of carriage path is read by optical pairLeaf Secondary Feedback – Ceramic Ball (Wiper) on each leaf arm provides contact pressure on a “Soft Potentiometer”Interlock PRO/SPRO :The MLC Controller compares the Secondary position of the leaf (Soft Pot) to its primary position (Motor Encoder Counts)
44 Gantry rotation control Prerequisite : From clutch drive to direct-driveConfiguration - Clinac console SW &+Clutchless drive & Velocity check enableChain tightnessSpeed : Aerotech Motor Control board. It drives the motor with a Pulse width modulated 100VDC (60s -0/+3s)
46 RapidArc® delivery of the TrueBeam® accelerator. What’s different?
47 RapidArc® delivery of the TrueBeam accelerator compared to Clinac) A TrueBeam system can deliver treatments up to 50% faster with a dose delivery rate of up to 2400 MU/minThe TrueBeam delivers 'gated' RapidArc radiotherapy, which compensates for tumor motion by synchronizing imaging with dose delivery during a continuous rotation around the patient.
48 TrueBeam OverviewThe Truebeam is a full integrated sytem
49 Thank you for your interest and attention QuestionsDiscussion
51 Optimize RapidArc delivery – Technical aspect Why a specific Machine QA ?During RapidArc:MLC leaves are movingGantry is rotatingDose rate is changing
52 Precision of the dose rate during gantry rotation ? Many questions?Precision of the dose rate during gantry rotation ?Accuracy of gantry speed control ?Ability to accurately vary the MLC leaves speed ?Accuracy of the MLC leaves positions ?Gravity effect / gantry angle?
56 VMAT / RapidArc testsSweeping gap ratio – Leaf gap Offset / dosimetry gapPicket fence (PF) Accuracy of DMLC positionStatic & during RapidArcDRGS : Ability to vary dose-rate and gantry speed7 combinations of dose rate, gantry range and speed to give equal dose to each stripDRMLC : Ability to accurately vary MLC leaf speed and dose rate.4 combinations of leaf speed and dose rate to give equal dose to each strip
62 Technical approach / optimization In a technical point of view what can we check ?The Mechanical performance (gantry, MLC)The Beam performance try to make a diagnostic in case of anomaly (beam or leaf related?)It is a separate approach, except for the absolute dosimetry calibration : Leaf Gap offset
64 The Mechanical performance (Clinac) GantryIsocenter check (Basic system QA)Chain correctly tightened (V7.11 & +). Check at few angles.
65 Gantry (Clinac) Bearing lubrification - every 2 years Gantry well balanced?Check current (GAN MOTI - check the gain 6.45)Check “Auto Go” function (no stop short, no oscillation).AMC, 4 adjustments (current limit, loop back gain, offset, speed)60s -0/+3s in both directions. If difference, check HCP / consoleReadout (PRO/SPRO).Replace the potmeters in case of frequent HWFA failures or “velocity check” errors. No backlash.Try to get the better “PRO calibration deviation” - Calibration
66 The Mechanical performance (Clinac) MLCOverview – main componentsSources of error?Isocenter calibration (basic QA)Mechanical backlash (Leaves, carriages)Leaf speed response, kinetic propertiesMLC calibrationDynalog ViewerHyperterminal Tests (Carriage & Leaves)
77 MLC CalibrationCalibration is performed at the time of installation and after any discrepancies in leaf positioning are foundAn Alignment tool (10 mm metal bar) is attached to the Collimator to perform Calibration of the Leaf BanksAn Infrared Optical beam in front of each carriage (when retracted) creates reference position for each leafEncoder Counts (information representing linear move of the leaf) are referenced to the optical beamCalibration process. Differences SW version 6.8 / 7.xMlcxcal.txt file (sw 6.8)diagAdjustSysOffsets command (sw 7.2+)
78 For rounded MLC leaf ends MLC CalibrationWARNING : don’t touch these parameters without knowing the consequencesSkewLeaf GapLightRadiationLeaf GapFor rounded MLC leaf endsCenterline
79 MLC Calibration Leaf Gap error / offset This parameter is directly linked to the Dosimetry Leaf Gap (TPS).Round leaf edge introduces additional transmission through the tip of the leaves.In the TPS, it is considered as an apparent gap between 2 closed leaves with non rounded edge.
81 Initialization Emitter gap 0.09mm A1 : Leading photodetector From Jiri Bocanek / VarianEmittergap0.09mmA1 : Leading photodetectorA2 : Trailing photodetectorWhen the signal of the leading detector is 50% of the signal of the trailing detector, the optical receiver asserts the Leaf-at-cal signal. At this point the MLC controller monitors (counts) the motor encoder signals.If the trailing photodetector is not receiving light from the infrared emitter, something is blocking the beam and the optical receiver asserts a Leaf-in-field signal.
82 Measurement of the optical beam – Opto Receiver MLC Optical beamWARNING : If adjustment or replacement of the emitter and/or the receiver are required, MLC leaf calibration, and therefore, MLC dose delivery could be affectedMeasurement of the optical beam – Opto ReceiverTP1 to TP2 = A1 minus A2TP2 to TP3 = A1 plus A2
83 Varian recommendations MLC Optical beamCTB-ML-570Varian recommendationsUse the detector value (TP2-TP3) alone to determine when to change the emitterIf the voltage (TP2-TP3) is less than 65mV, need emitter replacement and alignment.Always perform a full alignment procedure whenever any IR beam component is moved for any reason
84 MLC Dynalog File Viewer Use the Dynalog files as reference to monitor the wear of components. Check RMS data (average/Maximum/Histogram)ie : Use DLV, for the leaf speed test (acceptance of the RapidArc) or during other specific tests (QC).
85 Carriages : Varian recommendation (CTB-ML-422) Annually - Carriage Backlash Test - HyperterminalCommand: ws 2 for SW6.8, ws for SW7.x)Collimator 0°Gantry rotation from 180° every 90°Collect Carriage A & B secondary readout from controller (1/100th of mm)Difference between High and low values # 10Higher values indicate wear, or looseness of the primary bearing
86 Diagnostic commands Using the Hyperterminal Version 6.8 Software Version 7.x SoftwarediagPosILShow 2diagPosILShowdiagSecStatsShow 2diagSecStatsShowdiagMaxDeltaPriSecShow 2diagMaxDeltaPriSecShowdiagPriStallStatsShow 2
87 Leaf speedEach leaf speed should be similar to each other with a slight variation between the wider leaves and the thinner leavesEvery leaf must meet a minimum speed of 2.5 cm/sec at isocenter (1,275 cm/sec at leaf plane)Initialize the MLC and run the PWM testVersion 6.8 SoftwareVersion 7.x SoftwareInitializeCTRL+xwrPWM commanddiagLeafPWMTestMlc 2diagLeafPWMTestMlc
88 Leaf speed - PWM TestIf PWM < 12 for full leaves or PWM < 22 for half leaves, then no action is requiredIf PWM > 35 for full or half leaves, then cleaning or other service is requiredIf PWM is in between these values, then particular attention should be paid to leaves with significantly different values than the average.
89 Leaf speed - PWM TestHigh PWM values typically require leaf cleaning and/or leaf train component replacement.Adjacent pairs of leaves Dirty leavesIndividual leave Drive train component pb (excessive wear of the motor, drive screw…etc)Note : Higher PWM values (up to 2x) may be seen with CLL motors ( and ). Grey color cables, instead of black.Try to save all these diagnostic tests data for future comparison
90 Leaf Backlash test Position the gantry in the head-down position In Hyperterminal, run the following applicable diagnostic commandsVersion 6.8 SoftwareVersion 7.2 SoftwarediagLeafBacklashAll 2,1 (carriage A)diagLeafBacklashAll 1 (carriage A)diagLeafBacklashAll 2,2 (carriage B)diagLeafBacklashAll 2 (carriage B)
91 Leaf BacklashAnalyze the backlash values in the first column after the leaf numbers. Any values >0.200 require service. This typically requires leaf T-nut replacement
93 Leaf Touch Test – SW 7.xAfter a successful initialization, observe the Touch Test results at the bottom of the Hyper Terminal screen. Verify leaf gap values are less than +/ mm. If any of the leaf gap values are >+/-0.20 mm, the MLC system requires a realignment.Leaf gap errors >0.30 mm will result in initialization failures.
94 Beam performanceMachine QC: In case of an anomaly with DRGS, or DRMLC testsAll leaves? Beam or carriage?Beam quality – main parameters to controlHigh voltage (PFN / HVPSI) PFN servoGun emission (GunI)Hyper Frequency power (RF driver and AFC) AFC servo(no limitation on AFC, good system temperature)FWRPW / KLYI / Target current - flat shapes
95 Beam performance A good STARTUP of the beam is important. Dose rate stability % with and w/o the PFN servoDosimetry / POS & ANG servosNo difference of DR with close and open loops.Field light / Xray beam correct with closed loopsGantry rotation : No loss of DR (DR servo open)
96 Thank you for your interest and attention QuestionsDiscussion