1. RapidArc plan verification using ArcCHECK™
Dr Craig Edwards
University Hospital of North Staffordshire
The Cancer Centre,
Stoke-on-Trent,
Staffordshire,
ST4 6QG.
England

2. The University Hospital of North Staffordshire (UHNS)
Radiotherapy Physics;
Moved to the new Cancer Centre in June 2009
Cancer Centre features;
Eclipse treatment planning system
4 Varian iX linear accelerators
HDR Brachytherapy Unit
An Acuity simulator
GE lightspeed CT scanner

3. IMRT and RapidArc at UHNS
Dynamic IMRT 2005
Commissioned on 600C & 2100C Varian linacs
~ 15 patients per year (2:1 H&N:prostate)
Dynamic IMRT 2010
4 matched 2100iX Varian linacs
~ 175 patients per year (8:1 prostate:H&N)
have treated uterus, cordoma, breast
RapidArc 2011
Attended Varian training course
MSc Project
Commissioned patient QA system
First clinical patient summer 2011

4. IMRT IMRT = Intensity Modulated RadioTherapy
Modulate incident photon beam
Highly conformal technique
Mould dose around structures
Spare radio-sensitive structures
Increase delivered dose

5. Arc Therapy - RapidArc 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: cm/s
Dose rate: MU/min

6. Patient QA measurements
IMRT patient
Every field’s dose fluence measured and compared
Gamma analysis used to evaluate (3mm/3%)
Point dose measurement compared with expected (+/- 5%)
Arc Therapy
Replicate conventional IMRT ?

7. System Choice Several available Selection – ArcCheck ArcCheck Delta4
MatriXX / cube
Octavius
Selection – ArcCheck
Light
Single cable set-up
Absolute dose
Potentially 3D DVH mapping
looked right - cylindrical!!

8. Rotation QA system ArcCheck 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

9. Performance Tests Response reproducibility
Response linearity with dose
Dose rate dependence
Consistency of chamber response with orientation
Stability of calibration with time

10. 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
6 MV – 2.47 Gy (1.32 Gy at isocentre)
10 MV – 2.60 Gy (1.54 Gy at isocentre)

11. Response reproducibility
Method
Irradiated central diode
100 MU, 10 x 10 cm2 field
5 irradiations
Record response & compare with planning system
Determine coefficient of variation (CV)
Results
Mean reading cGy
Comparison with Eclipse %
Standard deviation: cGy
CV: %

12. Response linearity with dose
Method
Irradiated central diode
Varied delivered dose from 10 to 500 MU
10x10 cm2 field
Record response & compare with planning system
Determine CV

13. Response linearity with dose
Results
Comparison with Eclipse: max diff 0.3% MU)
above 100 MU, diff -0.1%
When normalised against 100 MU response;
Standard deviation: cGy
CV: %

14. Dose Rate Dependence Method 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)

15. Dose Rate Dependence Results Standard deviation: 0.70 cGy CV: 0.54 %
Comparison with Eclipse;
Maximum difference % MU.min-1)
Difference at 600MU.min %
Standard deviation: cGy
CV: %

16. Dependence upon irradiated angle
Method
Irradiated central diode
100 MU, 10 x 10 cm2 field
ArcCheck rotated to each angle
Record response
Determine coefficient of variation (CV)
Results
Mean reading cGy
Standard deviation: cGy
CV: %

17. Stability of calibration
Method
Irradiated central diode
100 MU, 10 x 10 cm2 field
Response recorded every 20 mins for 2 hours
Determine coefficient of variation (CV)
Results
Mean reading cGy
Standard deviation: cGy
CV: %

18. Clinical tests Verification of IMRT treatment
Verification of RapidArc treatment

19. Verification of IMRT Method 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%

20. Verification of IMRT Results Gamma evaluation pass rate 98.5 %
Point dose evaluation measured -0.2 %

21. Verification of RapidArc
Method
Same as IMRT except there is only 1 field!!

22. Verification of RapidArc
Results
Gamma evaluation shows 99.4 % pixel pass rate
Point dose evaluation measured -0.7 %

23. Conclusions The ArcCheck dosimetry system;
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