ESTRO 36 Abstract Book

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S283 ESTRO 36 2017
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Conclusion
The remote EPID based digital phantom method is feasible
for centres equipped with Varian linear accelerators
either Clinac or Truebeam. The methods to date for Elekta
systems require improvement before widespread use in
the remote audit.
OC-0538 A virtual dosimetry audit – towards
transferability between global QA groups in clinical
trials
M. Hussein1, D. Eaton 2, P. Greer3, A. Haworth4, C.
Hurkmans5, S. Ishikura6, S. Kry7, J. Lehmann4, J. Lye8, A.
Monti5, M. Nakamura6 , C. Clark2
1 Royal Surrey County Hospital NHS Foundation Trust,
Medical Physics, Guildford, United Kingdom
2 NCRI Radiotherapy Trials Quality Assurance Team,
RTTQA, London, United Kingdom
3 Calvary Mater Newcastle, Radiation Oncology Physics,
New South Wales, Australia
4 The Trans Tasman Radiation Oncology Group, TROG,
New South Wales, Australia
5 European Organisation for Research and Treatment of
Cancer, EORTC, Brussels, Belgium
6 The Japan Clinical Oncology Group JCOG, National
Cancer Center, Tokyo, Japan
7 Imaging and Radiation Oncology Core, IROC, National
Cancer Institute, USA
8 Australian Clinical Dosimetry Service ACDS, ARPANSA,
Victoria, Australia
Purpose or Objective
Quality assurance for clinical trials is important. Lack of
compliance can affect trial outcome. Different
international QA groups have different methods of dose
distribution verification and analysis, all with the ultimate
aim of ensuring compliance. As some clinical trials are
open to international recruitment, it is important to
understand how different analysis techniques and
tolerances translate between different groups. Therefore
the aim of this study was to gain a better understanding
of different process to inform potential future dosimetry
audit reciprocity.
Material and Methods
Six international radiotherapy clinical trial QA groups
participated. A treatment plan, using the 3DTPS test
virtual phantom (previously used in UK VMAT and
Tomotherapy Audit [1, 2]), was created using a 2 Arc VMAT
technique in Varian Eclipse 13.6 calculated using AAA. This
phantom has similar complexity to a head & neck cancer
case [1]. Each group was supplied with four datasets. The
first was a TPS reference dose cube. The remaining three
were simulated ‘Measured’ dose cubes, labelled 1 to 3.
These datasets were the original TPS plan with deliberate
errors introduced; including dose difference and MLC
positional errors. All data was exported in DICOM format
to be readable by any software. Users were blinded to the
measured data detail. Each group was requested to
perform an analysis on the datasets using their standard
technique for a typical head & neck plan (e.g. gamma
index analysis, Distance-to-Agreement (DTA), dose
difference, etc.) and to create their standard audit
report, including how the analysis was performed and
whether the ‘measurements’ pass or fail.
Results
Table 1 summarises analysis technique, software used,
acceptance criteria, and results for each ‘measured’
dataset. All but one group used the global gamma index
(γ) analysis. The remaining used the DTA analysis. For the
global γ there were differences in the normalisation
method (i.e. whether to use the maximum dose, a point
in a high dose low gradient region, etc.) and in pass/fail
criteria. Two groups had three decision levels for analysis;
optimal pass, mandatory pass and fail. The remainder had
straight pass/fail decision criteria. All groups passed
Measured 1 and 3. However, for Measured 2, four groups
recorded a pass, 1 passed but with further investigation
necessary, and 1 recorded a fail. Figure 2 shows an
example analysis of Measured 2.
Conclusion
For the same dataset, different international audit groups
had different analysis approaches and results. The results
of this study will lead to a better understanding of
methods and variability between audit groups and is
informative for future work focussing on analysis
techniques that are transferable between different
groups.
References
[1] Tsang Y et al BJR 2012;86:1022.
[2] Clark CH et al Radiother Oncol 2014;113:272-8.
OC-0539 A multicentre QA study on 4DCT and
IMRT/VMAT techniques for lung SBRT using a
respiratory phantom
M. Lambrecht1, J.J. Sonke2, M. Verheij2, C.W. Hurkmans1
1Catharina Ziekenhuis, Physics/Radiotherapy, Eindhoven,
The Netherlands
2Netherlands cancer institute, Radiotherapy,
Amsterdam, The Netherlands
Purpose or Objective
The EORTC has launched a phase II trial to assess efficacy
of SBRT for centrally located NSCLC: The EORTC—
LungTech trial. Due to neighbouring critical structures,
these tumours remain challenging to treat. To guarantee
accordance to protocol and treatment safety, an RTQA
procedure has been implemented within the frame of the
EORTC RTQA levels. To determine SBRT accuracy, we have
performed end-to-end tests investigating both 4D-CT and
IMRT/VMAT under static and respiratory conditions.
Material and Methods
All centres audited performed 3D-CTs and 4D-CTs on the
same phantom. It was successively scanned using two film
inserts, one with a 15mm diameter target (15mmd) and
one with a 25mm diameter target (25mmd). Three motions
were tested: 20bpm/15mm amplitude (A),
10bpm/15mmA, and 15bpm/25mmA. A test procedure
was developped to evaluate the impact of motion on the
target volume and motion as determined using the binned
CT data. These results were compared to the true volumes
and motion amplitudes. Regarding the credentialing of