ESTRO 36 Abstract Book

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S974 ESTRO 36 2017
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(contralateral mucosa, bladder, small bowel, sphincter,
prostate) were outlined by the same radiation oncologist
on two CT datasets; one with applicator for brachytherapy
planning, and the second without applicator for planning
for EBT modalities. For the EBT modalities, optimization
was performed in such a way to force the exact same CTV
coverage as was obtained for each patient treated with
HDREBT.
Results
Comparison of dose distributions in axial, coronal and
sagittal planes for one patient are given in Fig.1 (top) for
the three modalities investigated. Bottom of the Fig.1
shows comparison between DVH curves for the same
patient for CTV and three critical structures (bladder,
prostate, and sphincter). Table 1 summarizes averaged
(over 10 patients) dose distribution parameters for the
three modalities investigated.
Conclusion
From Fig.1 and Table 1 that both EBT modalities provide
very conformal dose distribution to the target while
providing generally better spearing of surrounding critical
structures except for the contralateral rectal wall. The
main advantage of brachytherapy is that there is no need
for additional PTV margin as the source moves together
with the rectum. However, our results suggest that even
the addition of PTV margins to sophisticated EBT
modalities can produce comparable (if not better) dose
distributions to brachytherapy plans. Although, all the EBT
modalities possess the image guided radiotherapy (IGRT)
systems that allow repositioning of the patient (hence
target) just before commencing the treatment fraction, it
is difficult to ascertain the impact of daily intra-treatment
rectal motility and gas interference on the CTV in this
study. The superior dose within HRCTV is best observed
with HDRBT and likely the most important factor for
achieving complete tumor response in the context of
organ preservation [Appelt et al, Int J Rad Oncol Biol Phys
2013; 85: 74-80].
EP-1799 Feasibility study of in vivo dosimetry with
optically stimulated dosimeters for 50kVp Papillon®
beam
C. Dejean1, A. Mana1, M. Gauthier1, J. Feuillade1, C.
Colnard1, J. Gérard1
1 Centre Antoine Lacassagne, Academic Physics, Nice,
France
Purpose or Objective
to evaluate optically stimulated luminescence dosimeters
(OSL, nanodot Landauer ™) to be used for in vivo dosimetry
with 50kVp beam.
Material and Methods
Papillon® mobile xray generator is delivering a 50kVp
treatment beam that can be used for skin or rectum
treatment. A new machine based on the same beam,
Papillon+® is being launched to add the opportunity of
delivering intra operative breast treatment.
OSL principle is to detect light emitted when the
luminescence material, which is exposed to radiation, is
stimulated with visible light. Associated reader is
Microstar ii.
Nanodots were irradiated with Papillon® beam treatment
to establish calibration curves and to evaluate
attenuation. Attenuation was measured by a second
nanodot situated under the first one wich is a pessimistic
way of determination as both plastic disk infused with
Aluminium oxide doped with Carbon Al2O3:C encased in a
plastic case.
Results
Detectors were read after irradiation from 10 to 22.5Gy.
No saturation was observed unlikely expected. Results
highlight a linear calibration curve with a regression linear
coefficient R²=0.9853.
Concerning attenuation, results are ranging from 80 to 70%
of reference measurements with this methodology.
Discussion: While dose used is in treatment range (around
20 Gy), linear calibration can be used which is different
from literature results. It may be linked to the evolution
made by Landauer concerning the Microstar reader
between (Price, Medical Physics 2013) and today. So, OSL
can be used at a time to evaluate skin dose but also
delivered dose at applicator surface.
Attenuation methodology needs to be modified to be more
relevant according to our clinical use. Gafchromic films
may be used to evaluate surface attenuation.
Conclusion
OSL nanodots are usable with 50kVp Papillon® beam for
breast intraoperative radiotherapy for example. OSL
reading is fast and without delay. Attenuation surface of
the detector is 0.9x0.9cmxcm that has to be clinically
validated before replacing thermoluminescence
dosimeters (TLD) classically used.
Uncertainties are on the same level as published one
concerning TLD (around 17%), they will determined with
Papillon+® beam that permits to treat breast in an
intraoperative mode.
EP-1800 Optical Fibre Luminescence Sensor for Real-
time LDR Brachytherapy Dosimetry
P. Woulfe1, S. O'Keeffe2, F.J. Sullivan3
1Woulfe Peter, Department of Radiotherapy, Galway,
Ireland
2University of Limerick, Optical Fibre Sensors Research
Centre, Limerick, Ireland
3National University of Ireland Galway, Prostate Cancer
Institute, Galway, Ireland
Purpose or Objective
This paper presents recent advancements in the
development of an optical fibre radioluminescence sensor
whereby the radiation sensitive scintillator, terbium-
doped gadolinium oxysulphide (Gd2O2S:Tb), is embedded
within the core of a 500µm PMMA (Polymethyl
methacrylate) plastic optical fibre. The reduced size of
the presented optical fibre sensor offers significant
advantages for application in brachytherapy. The small
dimensions of the sensor (less than 1mm including the
outer protective jacket) allows it to be easily guided
within existing brachytherapy equipment; for example,
within the seed implantation needle for direct tumour
dose analysis, in the urinary catheter to monitor urethral
dose, or within the biopsy needle holder of the transrectal
ultrasound probe to monitor rectal wall dose.
Material and Methods
The optical fibre sensor, shown in figure 1, is constructed
by micromachining a cavity in the 500µm core of a PMMA
(polymethyl methacrylate) plastic optical fibre. The