ESTRO 36 Abstract Book

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S86 ESTRO 36 2017
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tumour model under realistic, i.e. harsh, conditions at
experimental laser accelerators.
Results: Both human tumour models showed a high take
rate and continuous tumour growth after reaching a
volume of ~5 – 10 cubic millimetres. Moreover,
immunofluorescence analysis revealed that already the
small tumours interact with the surrounding tissue and
activate endothelial cells to form vessels. By analysing the
dose dependent tumour growth curves after 200 kV X-ray
treatment a realistic dose range, i.e. for inducing tumour
growth delay but not tumour control, was defined for both
tumour entities under investigation. Beside this basic
characterization, the comparison of the influence of laser-
driven and conventional (clinical Linac) electron beams on
the growth of FaDu tumours reveal no significant
difference in the radiation induced tumour growth delay.
Conclusion: The mouse ear tumour model was successfully
established and optimized providing stable tumour growth
with high take rate for two tumour entities (HNSCC,
glioblastoma) which are of interest for patient treatment
with protons. Experiments comparing laser-driven and
conventional proton beams in vivo as the next step
towards clinical application of laser-driven particle
acceleration are under way.
Acknowledgement: The work was supported by the
German Government, Federal Ministry of Education and
Research, grant nos. 03ZIK445 and 03Z1N511.
SP-0170 Novel models in particle biology research
P. Van Luijk1
1 van Luijk Peter, Department of Radiation Oncology,
Groningen, The Netherlands
The unique behaviour of particles that causes them to
reach maximum dose deposition at the end of their track
makes them useful for facilitating both treatment
intensification and reduction of normal tissue damage. On
a macroscopic scale particles facilitate reducing normal
tissue dose and irradiated volume. Though it has been
known for a long time that reducing the amount of
irradiated normal tissue reduces toxicity, the increased
precision of particles also makes sparing of substructures
possible and offers more flexibility in choosing how to
distribute inevitable excess dose over the normal tissues.
However, it is also these unique properties that limit the
information in available clinical data that can be used to
guide optimal use of particles. Filling this gap is an
important topic of particle radiobiology that has been
approached with various in vivo models.
On a microscopic scale particles deposit dose with a higher
ionization density, especially near the end of the particle
track, usually positioned in the target volume. Increased
ionization density has been demonstrated to change
response, both in terms of severity and potentially even in
type. These effects have been studied mostly in 2D in vitro
models. However, even though in 2D cell cultures
differential effects between high- and low-LET radiation
are observed, these models seem to be more
radiosensitive than one would expect based on clinical
data. Interestingly it has been observed that cells respond
markedly different when irradiated in a more tissue-
equivalent 3D culture system.
Moreover, recent insights from stem cell biology indicate
a potentially critical role of stem cells both in tumour and
normal tissue response. Taken together, 3D culture
systems based on tissue-specific stem cells may offer new
opportunities to better understand the response of
tumours and normal tissues to particle irradiation.
Proffered Papers: Prostate 1
OC-0171 Multiparametric MRI margin characterization
for focal brachytherapy in low-grade prostate cancer
S. Ken1, F. Arnaud1, R. Aziza2, D. Portalez 2, B. Malavaud3,
J. Bachaud4, P. Graff-Cailleaud4, S. Arnault 5, A. Lusque5,
T. Brun1
1Institut Universitaire du Cancer - Oncopole - Institut
Claudius Regaud, Medical Physics and Engineering,
Toulouse, France
2Institut Universitaire du Cancer - Oncopole - Institut
Claudius Regaud, Radiology, Toulouse, France
3Institut Universitaire du Cancer - Oncopole - CHU de
Toulouse, Urology, Toulouse, France
4Institut Universitaire du Cancer - Oncopole - Institut
Claudius Regaud, Radiotherapy, Toulouse, France
5Institut Universitaire du Cancer - Oncopole - Institut
Claudius Regaud, Bureau des Essais Cliniques, Toulouse,
France
Purpose or Objective
Focal brachytherapy is proposed in our institute as an
alternative treatment to active surveillance for low-grade
prostate cancer (PCa). This study aims at characterizing
the tumor focus and its margin with multiparametric
Magnetic Resonance Imaging (mpMRI) in order to prepare
the clinical protocol of focal brachytherapy.
Material and Methods
Patients pre-qualified for this study were positive for PCa
(Gleason 3+3) on a previous standard biopsy series. New
series of mp-MRI-guided and ultrasound-targeted biopsies
were performed and in total, 17 patients with confirmed
tumor and diameter<20mm were included in this phase II
clinical trial (NCT01902680). mpMRI were acquired on a
1.5T Magnetom Aera Siemens scanner with 18-channel
surface body coil. Anatomic imaging consists in Fast Spin
Echo T2-weighted MRI (T2-MRI). In addition, same in-
plane acquisition of functional Diffusion Weighted MRI
(DWI-MRI) and Dynamic Contrast Enhanced MRI (DCE-MRI)
were performed.
After mpMRI registration, tumor volumes of interest (VOI)
were drawn on anatomic T2-MRI. VOI and VOI+2mm were
reported on functional DWI-MRI and DCE-MRI (Figure 1).
Extracted parameters were Apparent Diffusion Coefficient
(ADC) and KTrans. All parameters distributions were
analyzed with Olea Sphere v3.0 and compared to
contralateral normal appearing tissue.
Focal brachytherapy was then delivered to all patients
with linked 125I seeds with a dose prescription of 152 Gy on
the Planning Target Volume (PTV=VOI+2mm).
Results
ADC parameters (mean, median, 25th and 75th
percentiles) are found to be significantly lower in tumor
volume (VOI) compared to contralateral normal tissue
(p<0.012 for all ADC parameters), confirming diffusion
tumor mass restriction. Different distributions of ADC and
Ktrans were observed among patients (Figure 2). Majority
(66.66%) of low ADC and abnormal Ktrans values were
included in the VOI. Interestingly, the 2mm margin allows
us to treat additional abnormal ADC and KTrans volumes
on 1/3 of the patients.