ESTRO 36 Abstract Book

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S242 ESTRO 36
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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. Pappas1, I. Kantemiris2, T. Boursianis3, G. Landry 4, G.
Dedes 4, T.G. Maris3, V. Lahanas5, M. Hillbrand6, K.
Parodi4, N. Papanikolaou7
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
Three hollow plexiglass cubes filled with VIPAR polymer
gel were produced and used in this study. Planning CT
scans of each one of the gel filled cubes and arbitrary
RStructures have been used for treatment planning. Cube-
1 was planned to be irradiated with mono-energetic
proton beams (90MeV & 115MeV) avoiding overlapping of
the irradiated gel areas (Max Dose : ~ 15 Gy). Cube-2 was
planned to be irradiated with a multi-energetic beam
forming a spread-out Bragg peak (SOBP) (Max Dose : ~ 13
Gy). Cube-3 was planned to be irradiated with two
opposing beams (Max Dose : ~ 13 Gy) each delivering an
overlapping and uniform SOBP. Set-up and irradiation of
each cube followed. One day post-irradiation each cube
was MRI scanned in order to derive high spatial resolution
3D-T2 maps that were subsequently co-registered to the
corresponding planning-CT scans and DICOM-RT Dose and
Structure data. Assuming a linear gel dose response, 1D,
2D and 3D dose measurements were derived and compared
against corresponding TPS data.
Results
VIPAR gel response seem to be non-dependent on LET for
LET values < ~6 keV/µm implying that their use for most
clinical cases is acceptable. No matter their LET
dependence, the protons range can be well verified. Even
if uncertainties related to imaging, set-up, beam delivery,
dose calculations, co-registration, gels LET dependence
were incorporated, the range measured by the proposed
method was within ~ 1 mm to that calculated by TPS.
Moreover, the corresponding ranges at the 80% value of
the maximum dose point for both TPS and polymer gels
derived percentage depth dose profiles (pdds) were equal
within ~1 mm. Additionally, for the opposed beams
experiment (cube-3), the proposed methodology results in
even more accurate dosimetry due to the reduced LET
values inside the SOBP compared to the high LET values
present in the irradiated schemes of cubes 1 and 2.
Conclusion
The proposed End-to-End Quality Assurance method based
on polymer gel dosimetry, provides valuable outcomes for
proton range verification and 3D proton dosimetry.
A. T2-map of the irradiated polymer gel cubic phantom,
co-registered to the corresponding planning-CT scans and
TPS calculated dose.
B. Pdd measurements
C. Isodoses in an arbitrary 2D plane
D. GI (5%dose/ 2mm criteria) calculated by the data
presented in C
First row: SOBP irradiation. Second row: Mono-energetic
115 MeV irradiation
Poster Viewing : Session 10: RTT
PV-0456 Volumetric Modulated Arc Therapy for
patients with bilateral breast cancer
S. Lutjeboer1, J.W.A. Rook1, G. Stiekema1, A.P.G. Crijns1,
N.M. Sijtsema1, E. Blokzijl1, J. Hietkamp1, J.A.
Langendijk1, A.J. Borden van der1, J.H. Maduro1
1UMCG University Medical Center Groningen, Radiation
Oncology, Groningen, The Netherlands