1. Mohammad Hussein Royal Surrey County Hospital, UK
A virtual dosimetry audit – towards transferability between global QA groups in clinical trials

2. A virtual dosimetry audit – towards transferability between global QA groups in clinical trials
M Hussein1, E Clementel2 , DJ Eaton3, P Greer4, A Haworth5, C Hurkmans2, S Ishikura6, SF Kry7, J Lehmann3, J Lye8, AF Monti5, M Nakamura6, CH Clark 1,3,9
1Royal Surrey County Hospital, UK, 2EORTC, Belgium, 3RTTQA, UK, 4 Calvary Mater Newcastle, Australia, 5TROG, Australia , 6JCOG, Japan, 7IROC, USA, 8ACDS, Australia, 9NPL, UK

3. / / The current process QA QA Group 2 Group 1 Hospital 2
TRIAL 1
TRIAL 2 QA
Group 1
Hospital 1 QA
Group 2
Hospital 2
/
/

4. / / / The current process QA QA Group 2 Group 1 Hospital 2
TRIAL 1
TRIAL 1 QA
Group 1
Hospital 1 QA
Group 2
Hospital 2
/
/
/

5. / The future process? QA QA Group 2 Group 1 Hospital 2 Hospital 1
TRIAL 1
TRIAL 1 QA
Group 1
Hospital 1 QA
Group 2
Hospital 2
/

6. Study Aim
To gain a better understanding of different dose distribution QA processes between different international groups
To inform potential future audit transferability

7. Methodology
6 international radiotherapy clinical trial QA groups participated
3 treatment plans generated in Varian Eclipse, 2.5mm dose grid, AAA v11.3 algorithm:
OAR
PTVs

8. Methodology Plans were copied and errors introduced
MLC positional errors, dose difference errors, gantry & collimator rotation errors
Ranged from subtle to significant
Each group was sent the original unedited planned dose labelled ‘TPS’, and the edited plans labelled ‘Measured 1’, ‘Measured 2’ etc.
All in DICOM format to be readable by any software
Users blinded to the ‘measured’ data details

9. 2nd stage In total the following were sent 3DTPS Test
5 ‘measured’ datasets
Prostate
Head & neck
7 ‘measured’ datasets

10. Examples

11. Gamma index analysis – groups’ own technique
Each group performed gamma analysis using their own routine settings for:
%dose / mm passing criteria
Global or local
Absolute or relative comparison
Normalise technique (e.g. max dose/point in high dose region etc.)
Lower dose threshold %

12. Summary of different analysis techniques
Audit group
Analysis technique used
Software
Standard Head & Neck plan Acceptance criteria 1
Global γ, absolute dose
CERR
7%/4mm
>85% points with γ<1
Prescription dose normalisation
no low dose threshold 2
SNC Patient v6.5.1
Optimal pass: 3%/2mm >90% points with γ<1
Mandatory pass: 3%/3mm >95% points with γ<1
Normalised to max dose
20% threshold 3
RIT version v5.0.0
3%/3mm
>95% points with γ<1
Normalised to a point in high dose low gradient region 4
In-house MATLAB software
>90% points with γ<1
30% threshold 5
PTW Verisoft v6.1.0
Optimal pass >97.5% points with γ<1
Mandatory pass > 90% with γ<1
Normalized to max dose 6
In-house MATLAB
software
10% threshold

13. Standardised gamma index analysis
Repeated the analysis using standard settings as follows:
2%/2mm, 3%/2mm, 3%/3mm, 5%/5mm, 7%/4mm
Global gamma
Absolute (i.e. no rescaling of datasets)
Gamma normalise point - max in ‘measured’ dataset
20% Lower dose threshold

14. Gamma passing rate per plan using each Group’s own technique
All 3%/3mm, except IROC (7%/4mm)

15. Gamma passing rate per plan using standardised parameters

16. 3%/3mm gamma passing rate per plan using standardised parameters

17. 3%/3mm gamma passing rate per plan using standardised parameters

18. Standardised gamma index analysis – MATLAB evaluation
Hussein, Clark & Nisbet (2017). Physica Medica;36:1-11

19. Standardised parameters – Matlab evaluation

20. Standardised parameters – Matlab evaluation 3%/3mm
Results from the 6 groups
Matlab

21. Mean gamma?

22. Summary
For the same virtual datasets, different international groups had different gamma analysis approaches and results
Differences were also in the standardised gamma index approach – these are due to different software implementations
This study only focussed on the software
Next step is to develop methodology to measure these plans on Varian linac by different groups to compare results
To inform future work focussing on analysis techniques that are transferable between different groups

23. Acknowledgments
Thanks to the authors at the 6 groups (ACDS, EORTC, IROC, JCOG, RTTQA, TROG) for their hard work and patience in processing the datasets
Thank you for listening
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