RapidArc plan verification
using ArcCHECK™
Dr Craig Edwards
University Hospital of North Staffordshire
The Cancer Centre,
Stoke-on-Trent,
Staffordshire,
ST4 6QG.
England
The University Hospital of North
Staffordshire (UHNS)
 Radiotherapy Physics;
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Moved to the new Cancer Centre in June 2009
 Cancer Centre features;
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Eclipse treatment planning system
4 Varian iX linear accelerators
HDR Brachytherapy Unit
An Acuity simulator
GE lightspeed CT scanner
IMRT and RapidArc at UHNS
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Dynamic IMRT 2005
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Dynamic IMRT 2010
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Commissioned on 600C & 2100C Varian linacs
~ 15 patients per year (2:1 H&N:prostate)
4 matched 2100iX Varian linacs
~ 175 patients per year (8:1 prostate:H&N)
have treated uterus, cordoma, breast
RapidArc 2011
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Attended Varian training course
MSc Project
Commissioned patient QA system
First clinical patient summer 2011
IMRT
 IMRT = Intensity Modulated RadioTherapy
 Modulate incident photon beam
 Highly conformal technique
 Mould dose around structures
 Spare radio-sensitive structures
 Increase delivered dose
Arc Therapy - RapidArc
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An advanced form of IMRT
Uses 177 control points
Gantry arm rotates 358°
Three forms of modulation
 Gantry speed: 0.5 – 4.8 °/s
 Leaf speed: 0 - 3 cm/s
 Dose rate: 0 - 600 MU/min
Patient QA measurements
• IMRT patient
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Every field’s dose fluence measured and compared
Gamma analysis used to evaluate (3mm/3%)
Point dose measurement compared with expected
(+/- 5%)
• Arc Therapy
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Replicate conventional IMRT ?
System Choice
• Several available
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ArcCheck
Delta4
MatriXX / cube
Octavius
• Selection – ArcCheck
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Light
Single cable set-up
Absolute dose
Potentially 3D DVH mapping
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looked right - cylindrical!!
Rotation QA system
• ArcCheck
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Cylindrical with diameter of 26.6 cm
Water equivalent
1386 diode detectors
Diodes at a depth of 2.9 cm
Diodes 1 cm apart
Arranged helically
Central cavity insert
Performance Tests
Response reproducibility
Response linearity with dose
Dose rate dependence
Consistency of chamber response with
orientation
• Stability of calibration with time
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Calibration
Varian 2100iX linear accelerator
Operating energies of 6 and 10 MV
Dose rate 600 MU.min-1
Field size 10 x 10 cm2
ArcCheck centre positioned at isocentre (SSD
86.7cm)
• 200 MU delivered
• Dose at detectors
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6 MV – 2.47 Gy (1.32 Gy at isocentre)
10 MV – 2.60 Gy (1.54 Gy at isocentre)
Response reproducibility
• Method
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Irradiated central diode
100 MU, 10 x 10 cm2 field
5 irradiations
Record response & compare with planning system
Determine coefficient of variation (CV)
• Results
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Mean reading
Comparison with Eclipse
Standard deviation:
CV:
129.71 cGy
- 0.15 %
0.13 cGy
0.10 %
Response linearity with dose
• Method
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Irradiated central diode
Varied delivered dose from 10 to 500 MU
10x10 cm2 field
Record response & compare with planning system
Determine CV
Response linearity with dose
• Results
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Comparison with Eclipse:
max diff 0.3% (@10 MU)
Linearity of response (10 MV)
above 100 MU, diff -0.1%
rec orded dos e (c G y )
700
600
 When
500 normalised against 100 MU response;
2
 400
Standard deviation:
0.38 cGy
 300
CV:
0.29 %
R = 1.00
200
100
0
0
100
200
300
delivered MU
400
500
Dose Rate Dependence
• Method
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Irradiated central diode
100 MU, 10 x 10 cm2 field
100 to 600 MU.min-1
Record response & compare with planning system
Determine coefficient of variation (CV)
Dose Rate Dependence
• Results
Dose rate dependence
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Comparison with Eclipse;
130.0
response (cGy)
129.8
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 Maximum difference
129.6
 Difference at 600MU.min-1
129.4
-1.4% (@100 MU.min-1)
-0.1%
129.2
Standard deviation:
129.0
0.70 cGy
128.8
128.6
CV:
0.54 %
128.4
128.2
128.0
0
100
200
300
dose rate (MU.min-1)
400
500
600
Dependence upon irradiated angle
• Method
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Irradiated central diode
100 MU, 10 x 10 cm2 field
ArcCheck rotated to each angle
Record response
Determine coefficient of variation (CV)
• Results
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Mean reading
Standard deviation:
CV:
129.52 cGy
0.68 cGy
0.50 %
Stability of calibration
• Method
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Irradiated central diode
100 MU, 10 x 10 cm2 field
Response recorded every 20 mins for 2 hours
Determine coefficient of variation (CV)
• Results
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Mean reading
Standard deviation:
CV:
129.72 cGy
0.23 cGy
0.18 %
Clinical tests
• Verification of IMRT treatment
• Verification of RapidArc treatment
Verification of IMRT
• Method
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ArcCheck CT scanned
Image used as template for verification plan
Export the treatment plan to ArcCheck image
Export re-calculated fluences MapCheck
Expected dose fluence compared to measured for
every field and the sum of all fields
Fields evaluated using gamma calculation with setting
of 3mm/3%
Verification of IMRT
• Results
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Gamma evaluation pass rate 98.5 %
Point dose evaluation measured -0.2 %
Verification of RapidArc
• Method
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Same as IMRT except there is only 1 field!!
Verification of RapidArc
• Results
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Gamma evaluation shows 99.4 % pixel pass rate
Point dose evaluation measured -0.7 %
Conclusions
• The ArcCheck dosimetry system;
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is simple and quick to set-up
has a quick and efficient software solution to
calibrate diodes in absolute dose
detectors demonstrated response characteristic
which would make it a suitable dosimetry tool
is an excellent solution for the verification of both
IMRT and RapidArc treatment