ESTRO 36 Abstract Book

535 / 1082

S520 ESTRO 36 2017
_______________________________________________________________________________________________
Material and Methods
The kinetic M1 model, is based on the spherical harmonic
expansion of the distribution function, solution of the
linear Boltzmann equation. The first two angular moments
equations, combined with the Continuous Slowing Down
Approximation, are closed using the Boltzmann's principle
of entropy maximization. The algorithm computes at the
same time all primary and secondary particles created by
the interactions of the beam with the medium. Thanks to
the implementation of the interaction cross sections for
electrons and photons in the energy range from 1keV up
to 100 MeV, the algorithm can simulate different
treatment techniques such as the external radiotherapy,
brachytherapy or intra-operative radiation therapy.
As a first validation step, a large number of heterogeneity
shapes has been defined for various complex numerical
phantoms both for electron and photon monoenergetic
sources. Dose profiles at different positions have been
measured in water phantoms including inhomogeneity of
bone ( ρ = 1.85 g/cm3), lung ( ρ = 0.3 g/cm3) and air ( ρ =
10-3 g/cm3). Secondly, taking as reference the Carleton
Laboratory for Radiotherapy Physics Database, different
radioactive seeds have been implemented in the code.
Moreover, several simulations based on CT scan of
prostate cancer have been performed. The M1 model is
validated with a comparison with a standard, accurate but
time consuming, statistical simulation tools as PENELOPE.
Results
The M1 code is capable of calculating 3D dose distribution
with 1mm 3 voxels without statistical uncertainties in few
seconds instead of several minutes as PENELOPE. Thanks
to its capability to take into account the presence of
inhomogeneities and strong density gradients, the dose
distributions significantly differ from those calculated
with the TG-43 approximations. More in detail: inter-seed
attenuation is treated, the real chemical composition of
the different tissues can be taken into account and the
effects of patient dimensions are considered.
Conclusion
In the comparison with the MC results the excellent
accuracy of the M1 model is demonstrated. In general, M1,
as the MC codes, overcomes the approximations that are
formalised in TG-43 in order to decrease the complexity
of the calculations. Thanks to its reduced computational
time and its accuracy M1 is a promising candidate to
become a real-time decision support tool for
brachytherapists.
PO-0947 Image-guided brachytherapy with 106Ru eye
plaques for uveal melanomas using post implantation
MRI
G. Heilemann1, N. Nesvacil2, M. Blaickner3, L. Fetty1, R.
Dunavoelgyi4, D. Georg2
1 Medical University of Vienna/ AKH Vienna, Department
for Radiotherapy, Vienna, Austria
2 Medical University of Vienna/ AKH Vienna, Department
for Radiotherapy/ Christian Doppler Laboratory for
Medical Radiation Research for Radiation Oncology,
Vienna, Austria
3 Austrian Institute of Technology GmbH, Health and
Environment Department Biomedical Systems, Vienna,
Austria
4 Medical University of Vienna/ AKH Vienna, Department
for Ophthalmology and Optometry, Vienna, Austria
Purpose or Objective
In radiation oncology magnetic-resonance imaging (MRI) is
an important modality for tissue characterization, target
delineation and allows image-guidance due to its high soft
tissue contrast as a tool for better cancer treatment. In
106Ru-brachytherapy of uveal melanomas MRI is mainly
used for pre-treatment planning scans to assess tumor size
and location. However, post-implantation MR scans yield
additional information on the plaque position in relation
to the target volume and critical structures. Together with
funduscopic images MRI can be used to better assess the
delivered doses to the target and the organs-at-risk (OAR).
The main goal of this feasibility study is to demonstrate
that fundus mapping and post implantation MR imaging
can be incorporated into the treatment planning workflow
of 106Ru plaque brachytherapy.
Material and Methods
Patients were scanned in a 0.35 T MR scanner (Magnetom
C! Siemens, Germany) after 106Ru eye plaque implantation.
To achieve a good normal tissue contrast for tumor
delineation and organ-at-risk (OAR) segmentation a fast
low angle shot (FLASH) T1 weighted sequence was utilized
(TR = 15 ms, flip-angles = 25°). A second FLASH MRI scan
with lower repetition times (TR = 11.2 ms) and flip-angles
(20°) was applied in order to display the plaque as a well-
defined void with minimal distortion artifacts at the cost
of lower signal to noise ratio and less soft tissue contrast.
Based on the MRI the resizable 3D eye model of a newly
developed treatment planning software (described in
detail in [1]) was adapted to the individual patient
anatomy in terms of size and plaque position.
Furthermore, the funduscopy image was projected onto
the retina of the digital 3D eye model.
Results
The presented method using two MR sequences yielded 3D
image sets that allowed segmenting both the anatomical
structures and the 106-Ru plaque. The funduscopy image
on the other hand is the optimal modality for tumor
segmentation. By combination the 3D eye model can be
adapted to match the individual patient and thus allow for
individual treatment planning and dose calculation (based
on MR anatomy) where the post-implantation imaging
accounts for the actual position of the plaque with respect
to the target and critical structures. This way irradiation
times can be calculated which guarantee full tumor
coverage. Moreover, the workflow can be applied for
treatment plan optimization strategies where plaques are
shifted in order to reduce doses to OARs.
Conclusion
In this feasibility study it was shown that MRI in
combination with funduscopy can be used to optimize
brachytherapy with 106Ru plaques. The additional spatial
information on plaque position relative to critical
structures, tumor geometry as well as position can be used
for more precise dose calculations and therefore improved
treatment planning.
References:
[1] G. Heilemann et al. Treatment plan optimization and
robustness of 106Ru eye plaque brachytherapy using a novel
software tool. Radiotherapy and Oncology. (in revision)
Poster: Brachytherapy: Miscellaneous
PO-0948 Role of HDR Intraluminal Brachytherapy in
carcinoma Esophagus: An institutional experience.
P.B. Kainthaje1, P. Gaur1, A. Malavat1, R. Paliwal1, V.
Sehra1
1Dr. Sampurnanand Medical College, Department of
Radiotherapy, Jodhpur, India
Purpose or Objective
To study the profile of patients of Carcinoma Esophagus
treated with Intraluminal Brachytherapy (ILBT), the
outcome of the treatment in terms of response
assessment, toxicity and survival.
Material and Methods
The study period was between January 2014 and June
2015, with 25 patients of carcinoma esophagus middle
third, treated with ILBT either as part of definitive
Radiotherapy or as part of palliative Radiotherapy. The
patients with unifocal disease ≤10cm in length and with no
recorded intra-abdominal or distant metastases received
definitive Radiotherapy with 44Gy/22Fr through EBRT with