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

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

/ / 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 / /

/ / / 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 / / /

/ 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 /

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

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

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

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

Examples

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 %

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

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

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

Gamma passing rate per plan using standardised parameters

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

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

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

Standardised parameters – Matlab evaluation

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

Mean gamma?

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

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 Questions / Comments