ESTRO 36 Abstract Book

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S240 ESTRO 36 2017
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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 der 1, J.H. Maduro1
1 UMCG University Medical Center Groningen, Radiation
Oncology, Groningen, The Netherlands
Purpose or Objective
The objective was to study the differences in target
coverage and dose-volume parameters for heart and lung
between Deep Inspiration Breath Hold (DIBH) 3D
Conformal Radiation Therapy (3D-CRT), DIBH Volumetric
Modulated Arc Therapy (VMAT) and free breathing
Intensity Modulated Radiation Therapy (IMRT) in patients
treated with synchronous bilateral breast cancer.
Material and Methods
This planning comparative study was conducted in nine
patients previously treated for synchronous bilateral
breast cancer. These patients were treated with either
DIBH 3D-CRT or IMRT in free breathing. All patients were
treated with whole breast irradiation and those requiring
a boost were given a simultaneously integrated boost
(SIB). Three treatment plans were constructed for each
patient individually; a DIBH 3D-CRT plan, a DIBH VMAT
plan and an IMRT plan in free breathing. DIBH IMRT is
clinically not feasible due to the extended duration of
treatment. Three patients were treated without a boost,
three were treated with unilateral SIB and the remaining
patients were treated with double sided SIB. DIBH 3D-CRT
plans were created using tangential fields for both breasts
and up to three boost fields for each breast, if a boost was
required. IMRT plans were created using 14 fields around
the patient, 24° apart, covering both breasts and
simultaneously covering the boost target in one or both
breasts. DIBH VMAT plans without boost targets were
created using eight 30° arcs, four on each side, oriented
in a tangential design. Four 60° arcs, in a tangential
design, were used in patients with boost targets, two for
each breast, with an additional semi-circle arc on either
side covering the boost targets. The parameters reviewed
were V95% (percentage of volume receiving 95% of the
prescription dose) PTV1 and PTV2 coverage, with PTV1
being the elective target and PTV2 the boost target, the
mean heart dose and heart left ventricle V5 (percentage
of volume receiving 5 Gy), mean lung dose, lung V5 and
lung V20. The parameters were compared using the paired
T-test for normally distributed data and the Wilcoxon
signed rank-test for not normally distributed data. Three
statistical analyses were performed on each parameter,
therefore the Bonferroni correction was applied. P≤0.016
was considered statistically significant in this study.
Results
Target coverage of PTV1 and PTV2 were comparable
between the three techniques (table 1), except the V95%
PTV1 left. All dose volume parameters of the heart and
lung were lower for the DIBH VMAT technique (table1) in
comparison with the DIBH 3D-CRT and free breathing IMRT
technique.
Conclusion
DIBH VMAT is the most optimal radiation technique in the
treatment for patients with synchronous bilateral breast
cancer. Both PTV coverage and the sparing of the organs
at risk give better results for DIBH VMAT in comparison
with DIBH 3D-CRT and IMRT in free breathing.
PV-0457 Delay between planning and stereotactic
radiotherapy for brain metastases: margins still
accurate?
C. Bonnet1, A. Dr Huchet1, E. Blais1, J. Dr Benech-Faure1,
R. Dr Trouette1, V. Dr Vendrely1
1Hopital Haut Leveque, Radiotherapy, Pessac, France