QA of cyberknife

1. M.RAMU (Medical Physicist)
RADIATION ONCOLOGY
MEDANTA-THE MEDICITY
GURGAON

2.  Daily QA in Linac and CyberKnife
 Machine output and Beam Data
Measurements withTolerance value.
Specification and it’sWorking Priniciple of QA
Tools such as:
 QA Beam Checker + -Standard imaging
 Penta-Guide Phantom – Qausar Modus
 AQA Phantom
 SRS profiler - Sun Nuclear corporation
 FC65-G ion Chamber - IBA

3.  Quality assurance is ‘ all those planned and
systematic actions necessary to provide
adequate confidence that a product or a
service will satisfy given requirements for
quality’
 It is a set of policies and procedures to
maintain the quality of patient care and
 as closely as possible to minimize the
oocurance of tratment mistakes caused by
equipment malfunction (or) human error.

4. Depends on vulnerability of QA parameters:
1. Daily
2. Weekly
3. Monthly
4. Yearly
5. On major repair and servicing
Daily test parameters, which could seriously
affect:
 Accurate patient positioning,
 Radiation field and target volume definition on
the patient surface (e.g., Lasers, ODI),

5.  GeneralTest: AudioVisual Monitor, Door
light/interlock,machine interlock,field
light,hand pendents,Daily backup.(Functional)
 MechanicalTest: ODI,LaserAlignment,fied size
matching (10x10cm²),MLC tests. (<1mm)
 Radiation/Output: Beam Energy, Field
Flatness,Symmetry,Output constancy. (<3%)
 CBCTTest: IsocentreAlignment of the couch
(Translation misalignment<2mm,rotation <1°) .

6. Procedure Tolerance
 Door interlock Functional
 Audio-visual monitor Functional
 Lasers 2 mm
 Optical distance indicator (ODI) 1.5 mm
 Output constancy (X & E) 3 %

7.  Use a solid phantom and set SPD=100cm.
Raise the phantom by 30 cm in steps of 1 cm
and record ODI readings. Bring back the
phantom to NTD and lower it by 20 cm in
steps of 1 cm and record the corresponding
ODI readings.All the readings must lie within
the given tolerance (± 1.5 mm)

8. S.No Distance Moved in cm ODI Readings
1 0 100
2 1 101
3 2 102
4 3 103
5 10 110
6 25 125
7 30 130

9.  Align Graph Paper with Cross-wires at collimator angle 0°
and SAD=100cm.
 Adjust the collimators to match several Field sizes (5x5cm²
to 40x40cm²) covering the clinical range.
 Verify that Field sizes defined by upper and lower jaws
respectively matches with the readings on the graph paper.
 Record the observations for both symmetric and asymmetric
motion of the jaws.
 Analyse the data to ensure that the results are within the
tolerence limit.
 Tolerance: 2mm or 1% of field width at isocenter for
symmetric motion of the jaws
 2mm on any side at iso for asymmetric motion of the jaws

10. Set optical Fs
(cmxcm)
Measure optical Fs
G.a (0°) (cmxcm)
Tolerance
5x5 5.0 For Fs ≤ 10x10cm²
±1 mm
10x10 10.0 &
15x15 15.1 For Fs ≥ 10x10cm²
≤ 2mm
20x20 20.15
25x25 25.1
30x30 30.1
35x35 35.12
40x40 40.16

11.  A precision alignment device for routine quality
control of lasers, linear accelerators and
simulators.
 Place the tool on the linac couch and use the
laser alignment marks with the room lasers to
align the Device at the isocenter.
 Check the laser alignment marks to ensure that
the room lasers are properly aligned or not .
 The positions between two laserpoints (Horiz
ontal&Vertical )corresponds to ±1mm.

13. Can be measured with any one of the following
method:
 With an ion chamber in a water tank
 With film inserted at reference depth in a
phantom
 With the beam profiler (diode array)
Record the average unflatness and asymmetry
over 80% of the field in the Beam profile.
Compare the results with the data obtained at
the time of commissioning.

14.  Obtain transverse beam profiles, at the
depths of dmax and 10 cm, along the two
orthogonal axes (X,Y) and diagonal axis of the
beam. Obtain maximum (Vmax ) and minimum
(Vmin ) values of dose in the central 80%
region of the respective beam profiles.
 Tolerance ≤ 3%
V=(Vmax -Vmin) / (Vmax +Vmin) * 100

15.  Definition: Beam profile is folded at the field
centre and two halfs of the profile are
compared.
 The ratio between measured values for each
pair of symmetrical points (with respect to
beam axis) for a range of field sizes and
gantry orientations must lie between .98 and
1.02 within the central 80% flattened beam
area.
 Tolerance: ±2%

16.  Measure the output of the machine for different
field sizes and available energy (Photons & e-) by
placing an ion chamber on the central axis in a
phantom at the depth of SSD + dmax (SAD=100cm )
 Normalise the values with respect to the
reference field size of 10 x 10 cm.
 Compare the measured output factors with the
baseline values.
 Output factor constancy should be checked for
each beam energy. Use gantry and collimator
angle: 0° for all measurements.
 Tolerance: ≤2%

17.  The ratio of the ionisation (J20 / J10)
measured at 20 cm and 10 cm depths
respectively for a field size of 10 cm x 10
cm,SSD=100cm. QI=J20/J10 <±1
Nominal Energy Quality Index( QI)
4MV 0.629 ± 0.015
6MV 0.676 ± 0.009
15MV 0.740 ± 0.001

21.  Uses to automatically determine which energy was
delivered (photons & e-).
 Verifying that the beam energy,fltness,symmetry,
output constancy and other parameters of the beam
are not changing over time.
 Inherent build up- for photons =3.5cm & for e-=1.5cm
 Onboard sencer- for temp and pressure corrections
 Wire Free mode- No cables
 Instant result , store in internal memory (512 data)
 Less time to measure and analysis of the datas

22.  Place on treatment couch, set F.S=20x20cm²
 SSD=100cm (infinity),SSD=125cm (16x16cm² -Syn).
 Make alignment using cross-wires and lasers.
 Power ON, Room select (1 or 2), maxi room select=9
 Delivered MU=100, Dose rate =400-600MU/min.
 expose it to the beam with any baselined energy,
and the front panel display will identify the energy,
give a pass/fail indication based on pre-configured
action levels.
 save this measurement to internal memory, and
automatically reset for the next exposure.
 At a later time, all measurement data can be
transferred to the PC for analysis and trending.

23. Output constancy:
Center (at time t) - Center (at time t0)/Center (at time t0 )
Time t -tima at which new constancy measrement is being taken
Time t0- time at which intial baseline value was teaken
Center (at time t) - Center (at time t0)
Center (at time t0 )
where:
time t time at which new constancy measurement is being takentime t0 time at which initial benchmark value was taken
Center (at time t) - Center (at time t0)
Center (at time t0 )
where:
time t time at which new constancy measurement is being takentime t0 time at which initial benchmark value was taken

24.  F.S=20x20cm², SSD=100cm, MU=100, Dose
rate=400MU/min,Temp & Pressure=!
Energy (MV) Flatness Axial
Symmetry
Transverse
Symmetry
4 1.3 -2.1 -0.1
6 0.9 -1.3 1.1
15 1.1 -1.0 0.5

25.  ASM- Axial Symmetry Out ofTolerance
 TSM –Trs.Symmetry Out ofTolerance
 FLT Flatness Out ofTolerance
 CST Constancy Out ofTolerance
 XXX Energy could not be determined

26.  Tests are related to
 (1) System safety,
 (2) Geometric accuracy, that is agreement of the
CBCT imaging isocenter with the isocenter of the
MV treatment beam,
 (3) Registration and correction accuracy, that is
how accurately can the system position a patient,
(4) Image quality, and
 (5) x-ray tube and generator performance (dose to
the patient).

27. Key Features :
 The QUASAR™ Penta-Guide ensures the accuracy of linac-
mounted image-guidance systems, including cone beam CT
(CBCT), x-ray volumetric imaging (XVI) and on-board imaging
(OBI), by enabling daily tests.
 Tests include the registration and alignment of crossed KV and
MV imaging systems and isocenter alignment of CBCT.
 Within the phantom there are 5 air filled spheres (A) and 5 low
density rings are placed (L &P).
 The use of airfilled spheres to ensure sufficient image contrast
without high density streak artificats.
 The spheres and rings are designed to appear on KV and MV
projection images of the phantom.

28.  Off-center Cross hairs-align with a point that is
known displacement from the center of the phantom.
 Level Indicator (A face)
 Isocenter cross hairs
 Bulls –eye rings
2,4,6,8,10 (mm dia)
for laser alignment.
 Useful for Laser & Light
field alignment 4x4; 10x10
;12x12 cm2

29.  The CBCTTests make use of a CT image of the Phantom
 These reference images are the standard against which
the daily A-P,R-Lat and CBCT images are compared.
 Place the P-G phantom at the isocenter of the CT
Scanner and acquire a CT scan of the Phantom.
 Export the CT scan to theTPS.
 Within theTPS place the isocenter at the center of the
Phantom (center of the central sphere).
 Export the plan to mosaiq and CT image to the CBCT
imaging system (XVI) and Save it for daily QA.

30.  Place the phantom on the linac couch and use
the laser alignment marks with the room lasers
to allign the phantom with the isocenter.
 Retract the KV source arm and Detector panal
 Set F.S=10cmx10cm,and Gantry angle=180 deg
 Tube potential=120KVp,T.Tube
current=1056.0mAs
 Nominal scan dose=22.0 mGy,
G.Speed=180/min
 Total no.of frames=660/360° (0.54°/frame)

31.  Aquire A-P and R-lat KV projection images of
the Phantom.
 Use automatic 2D image matching tool for
registration of the CBCT image with the
reference CT scan of the phantom.
 The registration tool will determine the x,y,z
discrepancy between the CBCT antTPS
isocenter. Record these values,typically this
offset should be <2mm in each direction

32.  Phantom centered in field of view, spheres
centered in rings

35.  Actual table move applied:
Table shift lat =0.00cm
Table shift long =0.05cm
Table shift vert =-0.26c
Clipbox alignment translation X Error =0.02cm
Clipbox alignment translationY Error =-0.08cm
Clipbox alignment translation Z Error =0.22cm
Clipbox alignment rotational X Error =0 deg
Clipbox alignment rotationalY Error =0 deg
Clipbox alignment rotational Z Error =0 deg

36.  Pre-Treatment check list (System OFF)
 Post-Treatment Chack list (System ON)
 Output Measurement (FC65-G ion chamber)
 Robot positioning Accuracy (AQA-Phantom)
 Beam data maesurements
(Flatness,Symmetry,Beam center,Penumbra
Width,Field size,laser and light field
coincidence) –using SRS Profiler
 Dose rate Measurement (MU/min)

38.  Check that all Emergency Stop (E-stop) are in
pulled out position.
 Check that theTreatment manipulator teach
pendant is in the proper mode.
 Check the pressure (30 ±2 psi) (2.1Kg/cm) of
SF6 gas and recharge if needed.
 Verify that the key (ESCC) is not turned to
Service Mode.
 Now ready to Power ON the CyberKnife Sys.

39.  Check the SF6 Gas pressure (28-32 psi)
 Check the Linac Gun HeaterVoltage (5.2±0.5V)
 Check the Linac Magnetic HeaterV (9.3± 0.5V)
 Check the Chiller waterTemp (19 ±1° C)
 Chech that all mechanical interlocks are active
 Verify that the treatment manipulator is positioned
in its perch position-usingTM teach pendant.
 Verify door interlocks and E-stops are enabled.
 Check water flow rate (>3 lit/min)

40.  Measurement Details:
 Chamber-FC65G Farmer chamber with 6MV
Buildup cap (1cm)
 Electrometer- SuperMax Standard Imaging
 SSD- 80cm in Birdcage
 Collimator Size- 60mm
 Temp&Pressure- 22°C & 997mb/hpa

42.  SensitiveVolume = 0.65cc
 Total Length = 150mm
 Diameter of inner electrode =1.0mm
 Length of the inner electrode =20.5mm
 Wall thickness of the buildup cap=3.1mm
(550mg/cm2)
 Outer diameter =7.1mm
 Stem length =65mm

43.  Outer electrode-Graphite (C) = 1.8 g/cmз
 Inner electrode-Aluminium = 2.7 g/cmз
 Chamber stem-Aluminium =2.7 g/cmз
 Build up cap POM(CH2O) =1.4 g/cmз
 Waterproof sleeve =Silicon
 Polarizing voltage/Guard Potential = ±300V
 Sensitivity = ~21x10-9 c/Gy

44.  Place the farmer chamber (FC65-G) with 1cm (6MV)
build up cap in Birdcage (SSD=80cm, C.F=6cm)
 Connect the chamber with superMax elctrometer.
 Make sure that the Linac has Fixed collimator(60mm)
 Measure autmosphericTemp & Air (ktp)
 Set biasVoltage (±300V), readout in Contineous mode
 Deliver MU=100
 Take atleast three meter readings (in nC) and correct
withTemp & Preasure (20.10 nC).
 Compare with baseline readings, it should be ≤2%

45.  (AQA) tool- measures the pointing accuracy of
the cyber knife system.
 Phantom made of acrylic (1.18g/cc) with
tungsten ball (3.5cm dia) under the cube for
attenuation (Eccentricity of the beam & shadow.
 It is working under the principle of Eccentricity.
 If the Eccentricity e =0 (circle) e= ≥0 (eclipse).

46.  Eccentricity (e) “is a Number that describes the
degree of the roundness of the Ellipse”.( e=0≤e≤1)
 Eccentricity (e) =ratio of the focal distance to major
axis / ratio of half of the focal distance to the semi-
major axis.
 Examble:.
 Th e semi-major axis is 10 and half of thefocal
distance is 5.
 So the eccentricity(e)=5/10=0.5 (it’s not circle) smaller
eccentricity rounder the circle
 e==0 , is circle. Ellipse >0 but <1.

48.  Place two orthogonal film (Gafchromic EBT3)
(AS &LS) in Phantom.
 Place the Phantom inTreatment couch using
room Laser for Alignment.
 Set fixed collimator =35mm,SSD=80cm
 A two path treatment (0° &90°) is delivered to
the film using different orthogonal X-ray
exposures.(KV=120,mAs=100).
 Acquire X-ray image and compare to the
reference image(DRRs) for robat positioning
accuracy.

49.  Film is scanned (film Scanner) and analyse is using
AQA software.
 It gives the Parameters like x-axis andY-axis
centroid shifts, Eccentricity,Radial error, etc for
both films.
 films were analyzed and Saved in detail for daily
variations.
 This particular test gives us information whether
the robot needs to be recalibrated or the scanner
needs replacement.
 Eccentricity (e)==0 for circle
Radial error= ≤ 0.6mm (smaller eccentricity,rounder
the circle)

51.  QA for stereotactic radiosurgery fields measuring multiple
beam parameters in a single exposure.
 Attaches to the Accuray® CyberKnife® birdcage.
 Real time analysis.
 Useful for measurement - Output, flatness, symmetry, field
size, beam center, penumbra width, Light:Radiation
coincidence.
 125 SunPoint® Diode Detectors (0.000019cc )
 Radial detector distribution
 Highest sensitivity (32.0 nC/Gy), smallest size(0.64mm2)
 Four axis geometry
 Central axis detector
 X,Y and diagonal axes
 4mm detector spacing with 2mm radial spacing.

54.  SRS PROFILER is fitted in the CybeKnife “birdcage”
it is firmly positioned at 80 cm SDD.
 The SRS PROFILER has field marks for 10, 20, 40,
60, 80, 100, and 120 mm circular fields,
 A computer with software is required to
communicate with the SRS PROFILER and display
the data.
 The cable connects the SRS PROFILER to the Power
Data Interface (PDI + 18V DC).
 software automatically detects the attached device
and configures the appropriate display.

55.  Fixed Collimator=60mm
 Additional buildup for 6MV=1g/cm² (inherent 0.5g/cm²)
 Deliver MU=100 Dose rate =1000Mu/min.
 SRS PROFILER is exposed to radiation, the software
instantly displays the acquired dose on the monitor.
 Frame capture (up to 20 frames per second) and play back
 It measured the beam measurents such as
 Centeral Axia dose,Flatness,Symmetry,Beam ceter,Field
size,Light and Radiation coincidence,penumbra.etc
 For SRS PROFILER, the gain is totally independent of the
selected machine dose rate, and only depends upon the
dose per pulse, which should not change unless the beam
energy or SSD changes.

56.  Field Size=5.99cm
 Beam center=0.01cm
 Penumbra (80/20)=!
 Flatness=110.1%
 Symmetry=100.2%
 CAX Dose=99.92cGy
 Light &radiation field coinc (6)

59. THANKYOU

60.  ACCEPTANCE/QUALITY ASSURANCETESTS FOR
MEDICAL LINEAR ACCELERATOR ( RPAD/ACC/QA/04)
 ACCURAY CYBERKNIFE MANUAL
 REFERENCE USER MANUALS AND IT’S WEB SITE OF
1. STANDARD IMAGING - QA BEAM CHECKER +
2. QUASAR MODUS –PENTA GUIDE PHANTOM
3. SUN NUCLEAR- SRS PROFILER
4. IBA-FC65-G FARMERTYPE CHAMBER