Transcript Rapid Arc - Ra-Workshop2012.dk

Workshop 2012
Serge Calippe -
European Technical Support HW
RapidArc® Workshop 2012
January 27-28th 2012, Aarhus, Denmark
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
Session 1a



RapidArc® – Basics
Technical description of RapidArc®
delivery on Clinac
RapidArc® delivery of the TrueBeam®
accelerator compared to Clinac)
RapidArc® – Basics
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
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
Technical description of
RapidArc® delivery on Clinac
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
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
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 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
RapidArc® – control points listing in Eclipse

Cumulative MU

Gantry Position

Dose Rate

Gantry Speed
Dicom RTplan

Abstract of a RapidArc® RTplan
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
Animation of variable dose delivered
to individual segments
RapidArc ® - Dose Rate & Gantry Speed Modulation
700
Dose rate [MU/min]
600
500
Dose Rate
Modulation
400
300
Gantry Speed
Modulation
Gantry Speed [deg/sec]
200
100
0
180
90
0
Gantry angle
270
180
RapidArc ® - Dose per Gantry Angle – MU/deg
2.5
2
Dose Rate
Modulation
MU/deg
1.5
1
Gantry Speed
Modulation
0.5
0
180
90
0
Gantry Angle [deg]
270
180
Technical description
RapidArc® on Clinac


Clinac controller maintains the relationship
between MU versus Gantry position
MLC controller maintains the MLC versus
Gantry position relationship
Technical description
RapidArc® on Clinac

MLC controller
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
Technical description
RapidArc® on Clinac

Variable gantry speed


Variable dose rate


0 – 600 MU/min
Variable dose per degree


0.5 – 4.8 degree/sec
0.2 – 20 MU/degree
Variable MLC speed

0 – 2.5 cm/s (5 mm/degree)
Note : It depends on energies / DR
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
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)
Dynamic MLC Arc log / Clinac Console
OOPS!! January 2008!!!
It is Not a RapidArc or VMAT Log!!!
RapidArc - VMAT Log File / Clinac Console
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

DiagAutoDynalogs 1 for SW 7.x
How to read?
MLC Log – Dynalog File viewer for SW6.8
MLC Log – Dynalog File viewer for SW7.x
MLC Log - Example
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)
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.
Gridded GUN
-
HE Clinac - Injection OFF
Gridded GUN
-
HE Clinac - Injection ON
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
Gridded GUN
-
HE Clinac
Gridded GUN

-
HE Clinac
Injection pulses are coincident or delayed to
RF pulses to produce beam pulses or not,
based on the segments window.
Control of the Dose rate
Gun controller
KLY Current signal
Used as the pulse Reference
Constant time relationship to
RF power in the guide.
PULSE CONTROL
GUN CONTROLLER
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
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
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)
Gantry rotation control

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)
Gantry rotation control – clutchless drive
RapidArc® delivery of the
TrueBeam® accelerator.
What’s different?
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.
TrueBeam Overview

The Truebeam is a full integrated sytem
Thank you for your interest
and attention
Questions
Discussion
Session 1b

Optimize RapidArc delivery – Technical
aspect




Why a Machine QA ?
Hardware and software adjustments (MLC
– Gantry – Beam performance)
PMI / (Tests, dynalog files)
Discussion
Optimize RapidArc delivery – Technical aspect

Why a specific Machine QA ?
During RapidArc:

MLC leaves are moving

Gantry is rotating

Dose rate is changing
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?
Article Commissioning - Machine QA
Machine QA – TPS / Patient QA
VMAT / RapidArc tests

Sweeping gap ratio – Leaf gap Offset / dosimetry gap

Picket fence (PF) Accuracy of DMLC position


DRGS : Ability to vary dose-rate and gantry speed


Static & during RapidArc
7 combinations of dose rate, gantry range and
speed to give equal dose to each strip
DRMLC : 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
Tests plans on MyVarian.com
Article on machine QA EPID-based
FOLLOWING ILLUSTRATIONS FROM THIS ARTICLE
Picket fence Test
DRGS Test
DRMLC Test
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
CTB-GE-725
The Mechanical performance (Clinac)

Gantry


Isocenter check (Basic system QA)
Chain correctly tightened (V7.11 & +). Check at
few angles.
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 / console
Readout (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
The Mechanical performance (Clinac)

MLC

Overview – main components

Sources of error?

Isocenter calibration (basic QA)

Mechanical backlash (Leaves, carriages)

Leaf speed response, kinetic properties

MLC calibration

Dynalog Viewer

Hyperterminal Tests (Carriage & Leaves)
MLC - CTB-ML-422-F
MLC OVERVIEW
MLC OVERVIEW – main components
Carriage – Rails / bearing
MLC Carriages
Motors interconnect
Motor / Encoder – Lead screw / bearing / T-nut
Leaf assembly
T-nut
Ceramic ball for sec readout
Spring
Drive screw
Motor
Coupler
MLC Calibration
MLC Calibration
MLC Calibration





Calibration is performed at the time of installation and
after any discrepancies in leaf positioning are found
An Alignment tool (10 mm metal bar) is attached to the
Collimator to perform Calibration of the Leaf Banks
An Infrared Optical beam in front of each carriage (when
retracted) creates reference position for each leaf
Encoder Counts (information representing linear move of
the leaf) are referenced to the optical beam
Calibration process. Differences SW version 6.8 / 7.x

Mlcxcal.txt file (sw 6.8)

diagAdjustSysOffsets command (sw 7.2+)
MLC Calibration
Skew
WARNING : don’t touch these
parameters without knowing the
consequences
Leaf Gap
Light
Radiation
Leaf Gap
For rounded
MLC leaf ends
Centerline
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.
MLC Optical beam
Initialization
From Jiri Bocanek / Varian
Emitter
A1 : Leading
photodetector
gap
0.09mm
A2 : Trailing
photodetector
When 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.
MLC Optical beam


WARNING : If adjustment or replacement of the
emitter and/or the receiver are required, MLC
leaf calibration, and therefore, MLC dose
delivery could be affected
Measurement of the optical beam – Opto Receiver

TP1 to TP2 = A1 minus A2

TP2 to TP3 = A1 plus A2
MLC Optical beam

CTB-ML-570

Varian recommendations



Use the detector value (TP2-TP3) alone to
determine when to change the emitter
If 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
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).
Carriages : Varian recommendation (CTB-ML-422)

Annually - Carriage Backlash Test - Hyperterminal

Command: 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 # 10
Higher values indicate wear, or looseness of the
primary bearing
Diagnostic commands

Using the Hyperterminal
Version 6.8 Software
Version 7.x Software
diagPosILShow 2
diagPosILShow
diagSecStatsShow 2
diagSecStatsShow
diagMaxDeltaPriSecShow 2
diagMaxDeltaPriSecShow
diagPriStallStatsShow 2
Leaf speed



Each leaf speed should be similar to each other with a
slight variation between the wider leaves and the
thinner leaves
Every 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 test
Version 6.8 Software
Version 7.x Software
Initialize
CTRL+x
wr
PWM command
diagLeafPWMTestMlc 2
diagLeafPWMTestMlc
Leaf speed - PWM Test

If PWM < 12 for full leaves or PWM < 22 for half leaves, then no action is required

If PWM > 35 for full or half leaves, then cleaning or other service is required

If PWM is in between these values, then particular attention should be paid to
leaves with significantly different values than the average.
Leaf speed - PWM Test

High PWM values typically require leaf cleaning
and/or leaf train component replacement.




Adjacent pairs of leaves  Dirty leaves
Individual 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 (1105360-09 and 1105182-07). Grey
color cables, instead of black.
Try to save all these diagnostic tests data for future
comparison
Leaf Backlash test


Position the gantry in the head-down position
In Hyperterminal, run the following applicable
diagnostic commands
Version 6.8 Software
Version 7.2 Software
diagLeafBacklashAll 2,1
(carriage A)
diagLeafBacklashAll 1
(carriage A)
diagLeafBacklashAll 2,2
(carriage B)
diagLeafBacklashAll 2
(carriage B)
Leaf Backlash
Analyze the backlash values in the first column after the leaf
numbers. Any values >0.200 require service. This typically
requires leaf T-nut replacement
Statistical Data Analysis
Leaf Touch Test – SW 7.x


After a successful initialization, observe the Touch Test results at the
bottom of the Hyper Terminal screen. Verify leaf gap values are less
than +/- 0.20 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.
Beam performance

Machine QC: In case of an anomaly with DRGS, or DRMLC tests


All leaves? Beam or carriage?
Beam quality – main parameters to control

High voltage (PFN / HVPSI)  PFN servo

Gun emission (GunI)

Hyper Frequency power (RF driver and AFC) AFC servo
(no limitation on AFC, good system temperature)

FWRPW / KLYI / Target current - flat shapes
Beam performance

A good STARTUP of the beam is important.

Dose rate stability +15-18% with and w/o the PFN servo

Dosimetry / POS & ANG servos


No difference of DR with close and open loops.

Field light / Xray beam correct with closed loops
Gantry rotation : No loss of DR (DR servo open)
Thank you for your interest
and attention
Questions
Discussion