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Workshop 2012

Workshop 2012. Serge Calippe - European Technical Support HW RapidArc ® Workshop 2012 January 27-28 th 2012, Aarhus, Denmark. Session 1a RapidArc ® – Basics Technical description of RapidArc ® delivery on Clinac RapidArc ® delivery of the TrueBeam ® accelerator Discussion Session 1b

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Workshop 2012

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  1. Workshop 2012 Serge Calippe - European Technical Support HW RapidArc®Workshop 2012January 27-28th 2012, Aarhus, Denmark

  2. Session 1a • RapidArc®– Basics • Technical description of RapidArc®delivery on Clinac • RapidArc®delivery of the TrueBeam® accelerator • Discussion Session 1b • Optimize RapidArc®delivery – Technical aspect • Why a specific Machine QC ? • Hardware and software adjustments (MLC – Gantry – Beam performance) • PMI / Machine QC (Tests, dynalog files) • Discussion

  3. Session 1a • RapidArc®– Basics • Technical description of RapidArc®delivery on Clinac • RapidArc®delivery of the TrueBeam®accelerator compared to Clinac)

  4. RapidArc®– Basics

  5. RapidArc® – Basics • RapidArc® 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 Linac • Substantially 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 speed • MLC leaves are allowed to travel in and out + leaf Interdigitation capabilities • The arc optimization algorithm, PRO (Progressive Resolution Optimizer), ensures the treatment precision. It optimizes leaf position, dose rate and gantry speed Demo..\RapidArc_Treatment_Timing.mp4

  7. Technical description of RapidArc®delivery on Clinac

  8. Technical description RapidArc® on Clinac • Operation and Control • Functioning of the Clinac control system during RapidArc®delivery • Synchronization of MLC, gantry and dose rate • Constraints

  9. Technical description RapidArc® on Clinac • A full arc is divided in simple segments defined by control points. • Parameters to control? • Gantry angle • Dose delivered / dose rate • MLC leaves positions • Each 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 ResolutionOptimizer-PRO) • 1 segment every # 2 degrees for a full turn. • For each single segment: • Dose rate is constant • Gantry speed is constant • Starting and ending of MLC leaves are known • Gantry, MLC and MUs are monitored every 50ms • Dose rate or gantry speed are adjusted if needed

  11. RapidArc®– control points listing in Eclipse • Cumulative MU • Gantry Position • Dose Rate • Gantry Speed

  12. DicomRTplan • Abstract of a RapidArc®RTplan

  13. Technical description RapidArc® on Clinac • The RapidArc®plan is moded up through the 4DITC, and is then divided in two groups of control parameters • The 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 beam • The treatment delivery is controlled by the Clinac controller and the MLC controller

  14. Animation of variable dose delivered to individual segments

  15. RapidArc ®- Dose Rate & Gantry Speed Modulation Dose Rate Modulation Gantry Speed Modulation Gantry Speed [deg/sec]

  16. RapidArc ®- Dose per Gantry Angle – MU/deg Dose Rate Modulation Gantry Speed Modulation

  17. Technical descriptionRapidArc® on Clinac • Clinaccontroller maintains the relationship between MU versus Gantry position • MLC controller maintains the MLC versus Gantry position relationship

  18. Technical description RapidArc® on Clinac • MLC controller

  19. Technical description RapidArc® on Clinac • Gantry speed must slow down so that the MLC leaves can catch up to the specified leaf positions • Maximum treatment time depends on complexity of the treatment plan • Gantry must slows down to deliver lots of doses or MUs or increase MU rate • To maximize treatment time, use lower prescribed dose or maximum MU rate

  20. Technical description RapidArc® on Clinac • Variable gantry speed • 0.5 – 4.8 degree/sec • Variable dose rate • 0 – 600 MU/min • Variable dose per degree • 0.2 – 20 MU/degree • Variable MLC speed • 0 – 2.5 cm/s (5 mm/degree) Note : It depends on energies / DR

  21. Technical description RapidArc® on Clinac • Arcs / plan* • Total arc / plan* • Min arc* • Segments may be avoided • Max dose : 7200 MU • 9999 MU for 6X SRS (7.9+) *Note : It depends on SW releases

  22. LOG Files • During the treatment, the system can generate Logs: • Clinac console (Communication/Log): Generation of a Dynamic beam delivery Log • 4DITC WS : Generation of a MLC log (2 files Carriages A & B)

  23. Dynamic MLC Arc log / Clinac Console OOPS!! January 2008!!! It is Not a RapidArcor VMAT Log!!!

  24. RapidArc- VMAT Log File / Clinac Console

  25. MLC Log – Dynalog File Viewer • Dynamic leaf deviation • Log 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 6.8 • DiagAutoDynalogs1for SW 7.x • How to read?

  26. MLC Log – Dynalog File viewer for SW6.8

  27. MLC Log – Dynalog File viewer for SW7.x

  28. MLC Log - Example

  29. Control of the Dose rate • Fastbeam-on / beam-off control. • On highenergyClinac : the keyis the triode gridded gun (On Unique system : magnetronfrequency)

  30. Control of the Dose rate • On high Energy Clinac the gridded electron gun allows Instantaneous dose rate control • The cathode is heated to excite emissions of electrons. The injection is controlled by the grid.

  31. Gridded GUN - HE Clinac - Injection OFF

  32. Gridded GUN - HE Clinac - Injection ON

  33. Gridded GUN - HE Clinac • The 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 emission • This gives us a very precise control so we can terminate or start the gun’s electron flow as required

  34. Gridded GUN - HE Clinac

  35. Gridded GUN - HE Clinac • Injection pulses are coincident or delayed to RF pulses to produce beam pulses or not, based on the segments window.

  36. Control of the Dose rate

  37. Gun controller KLY Current signal Used as the pulse Reference Constant time relationship to RF power in the guide. PULSE CONTROL GUN CONTROLLER

  38. MLC • The MLC workstation integrated in the 4DITC, sends data for entire treatment for all leaves, including dose versus position information, to MLC Controller via serial link • MLC Controller will set MLC leaves in place • Upon start of treatment, MLC Controller sends commands to MLC head via optical link to move leaves • MLC Controller compares planned and actual position of each leaf obtained from feedback system with the treatment plan

  39. MLC - Primary Readout System • Leaf Position is determined using 2 independent sources • Primary Readout utilizes encoder mechanically attached to motor’s shaft for both carriages and leafs • Carriage • 540 counts = 1 mm of linear shift at isocenter • Leaf • 707 counts = 1 mm linear shift for full width leafs • 512 counts = 1 mm linear shift for half width leafs at isocenter

  40. MLC - Secondary Readout System / Interlock • Secondary Feedback verifies, that motor count really represents actual motion • Carriage – Mylar strip with fine black lines at the side of carriage path is read by optical pair • Leaf 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)

  41. Gantry rotationcontrol • Prerequisite : From clutch drive to direct-drive • Configuration - Clinac console SW 7.8 - 7.9 - 7.11 &+ • Clutchless drive & Velocity check enable • Chain tightness • Speed : Aerotech Motor Control board.It drives the motor with a Pulse width modulated 100VDC (60s -0/+3s)

  42. Gantry rotation control – clutchless drive

  43. RapidArc® delivery of the TrueBeam® accelerator. What’s different?

  44. 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/min • The TrueBeam delivers 'gated' RapidArc radiotherapy, which compensates for tumor motion by synchronizing imaging with dose delivery during a continuous rotation around the patient.  

  45. TrueBeam Overview • The Truebeam is a full integrated sytem

  46. Thank you for your interest and attention Questions Discussion

  47. Session 1b • Optimize RapidArc delivery – Technical aspect • Why a Machine QA ? • Hardware and software adjustments (MLC – Gantry – Beam performance) • PMI / (Tests, dynalog files) • Discussion

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