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TV coverage. To avoid the common mistakes encountered,
a new approach to training including verbal instructions is
being developed for testing. Our aim is to demonstrate
benefits in clinical workflow and expand validation to
other RT centres.
OC-0453 Stereotactic radiosurgery for multiple brain
metastases: Results of multi-centre benchmark studies
D.J. Eaton
1
, J. Lee
1
1
Radiotherapy Trials QA group RTTQA, Mount Vernon
Hospital, Northwood, United Kingdom
Purpose or Objective
Stereotactic radiosurgery (SRS) is strongly indicated for
treatment of multiple brain metastases. Various
treatment platforms are available, and comparisons have
been made between modalities, but mostly in single
centre studies. A pre-requisite for all providers selected
as SRS/SRT centres in England was to participate in a
quality assurance process, informed through collaboration
between the national trials QA group and a
multidisciplinary expert advisory group. All clinical
centres undertook planning benchmark cases, providing a
unique dataset of current practice across a large number
of providers and a wide range of equipment. This was used
to facilitate sharing of best practice and support centres
with less experience.
Material and Methods
Two brain metastases cases were provided, wit h images
and structures pre-drawn, involving three and seven
lesions respectively. Centres produced plans a ccording to
their local practice, and these were reviewed centrally
using metrics for target coverage, selectivity, gradient
fall-off and normal tissue sparing.
Results
38 plans were submitted, using 21 differe nt treatment
platforms, including Gamma Knife, Cyberknife, Varian
(Novalis / Truebeam STx / 2100), Elekta (Synergy / Versa
HD using Beam Modulator / Agility MLC) and Tomotherapy.
6 plans were subsequently revised following feedback, and
review of 4 plans led to a restriction of service in 3
centres. Prescription doses were typically 18-25Gy in 1
fraction (or 27/3fr), except for a lesion within the
brainstem, which was prescribed 12-20Gy in 1 fraction (or
18-30Gy/5fr). All centres prioritised coverage, with the
prescription isodose covering ≥95% of 208/209 lesions.
Selectivity was much more variable, especially for smaller
lesions, and in some cases this was combined with high
gradient index, resulting in large volumes of normal tissue
being irradiated. Both Tomotherapy submissions were
outliers in terms of either selectivity or gradient index,
but all other platforms were able to give plans with
relatively low gradient indices for larger lesion volumes,
although there was more variation among Varian and
Elekta plans, than for Gamma Knife and Cyberknife (first
figure). There were also larger differences for the smaller
volumes, with increasing variation both inter- and intra-
treatment-platform. Doses to normal brain and brainstem
were highest when PTV margins were applied, but
substantial improvements were possible by re-planning,
even without changing margin size (second figure).
Conclusion
These benchmarking exercises give confidence in the safe
and consistent delivery of SRS services across multiple
centres, but have highlighted areas of different priorities,
and potential for service improvement. The data can be
used to progress standardisation and quality improvement
of national services in the future, and may also provide
useful guidance for centres worldwide.
OC-0454 End-to-end QA methodology for proton range
verification based on 3D-polymer gel MRI dosimetry
E. Pappas
1
, I. Kantemiris
2
, T. Boursianis
3
, G. Landry
4
, G.
Dedes
4
, T.G. Maris
3
, V. Lahanas
5
, M. Hillbrand
6
, K.
Parodi
4
, N. Papanikolaou
7
1
Technological Educational Institute of Athens higher
education, Radiology/Radiotherapy Technologists,
ATHENS, Greece
2
Metropolitan Hospital, Medical Physics Department-
Radiation Oncology Division, Athens, Greece
3
Medical School- University of Crete, Department of
Medical Physics, Heraklion, Greece
4
Ludwig-Maximilians-Universität München, Department
of Medical Physics, Munich, Germany
5
National and Kapodistrian University of Athens, Medical
Physics Laboratory - Simulation Center-, Athens, Greece
6
Rinecker Proton Therapy Center, Department of Medical
Physics, Munich, Germany
7
University of Texas Health Science Center, Department
of Radiation Oncology-, San Antonio- Texas, USA
Purpose or Objective
In clinical proton therapy, proton range measurements are
associated with considerable uncertainties related to : a)
imaging, b) patient set-up, c) beam delivery and d) dose
calculations. A sophisticated QA process that can to take
into account all the mentioned sources of uncertainties is
required in clinical practice. In this work, cubic phantoms
filled with VIPAR polymer gels have been used towards this
aim. An investigation of the gels dosimetric performance
and their potential use for proton dosimetry purposes and
as an end-to-end QA method for proton range verification
has been implemented.
Material and Methods