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S407
ESTRO 36 2017
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PO-0776 Thermoluminescence Characteristics of
Fabricated Ge Doped Optical Fibre for Radiotherapy
Dosimetry
M.S. Ahmad Fadzil
1
, N. Tamchek
2
, N.M. Ung
3
, A. Ariffin
4
,
N. Abdullah
5
, D.A. Bradley
6
, N. Mohd Noor
1
1
Universiti Putra Malaysia, Department of Imaging-
Faculty of Medicine and Health Sciences, Serdang,
Malaysia
2
Universiti Putra Malaysia, Department of Physics-
Faculty of Science, Serdang, Malaysia
3
University of Malaya, Clinical Oncology Unit- Faculty of
Medicine, Kuala Lumpur, Malaysia
4
University of Malaya, Department of Physics- Faculty of
Science, Kuala Lumpur, Malaysia
5
Malaysia Nuclear Agency, Medical Physics Group,
Kajang, Malaysia
6
University of Surrey, Department of Physics, Guildford,
United Kingdom
Purpose or Objective
The dosimetry characteristics of the fabricated
Germanium doped cylindrical fibre (CF) and flat fibres (FF)
were evaluated including linearity, repeatability, energy
dependence, dose rate dependence, angular dependence
and fading. The TL kinetic parameters of Ge-doped CF and
FF have been investigated using the computerized glow
curve deconvolution analysis.
Material and Methods
A screening process was carried out for the optical fibres
with 6 MV photon beam. Optical fibres with sensitivity out
of ±5% mean sensitivity value were discarded in order to
ensure the selected dosimeters have constant response.
The dosimetry characteristics tests were performed using
6 MV and 10 MV photon beams. The dosimeters were
irradiated with doses ranging from 1 Gy to 3 Gy with
several dose rates (100 MU/min up to 500 MU/min).
Fabricated perspex phantoms were used to study the
angular dependency of the optical fibres. Fading rate was
studied for 55 days post irradiation. The glow curves were
analyzed with a curve fitting computer program known as
WinGCF. The glow curves were deconvoluted into five
individual peaks in order to figure out the kinetic
parameters such as the maximum peak temperature
(
T
max
), peak integral (
PI
), activation energy (
E
a
) and
frequency factor.
Results
The screening result revealed that the coefficient of
variation was observed to be less than ±10% for CF and FF.
Both CF and FF were found to be linear with r
2
more than
0.99 over the entire dose range explored for both 6 MV and
10 MV photon beams. These fibres provide consistent
reading within ±5% over five repeated measurements. The
signal lost was higher in FF (57%) compare to CF (38%) after
55 days of irradiation. Both fibres also offer dose rate- and
angular independence. The glow curve for both CF and FF
consist of 5 individual glow peaks. The peak height
increased with increasing irradiation dose. The T
max
of the
glow peaks (P1 to P5) is consistent over the dose range
used
.
Peak 1 has the lowest E
a
which lies between 0.544
to 0.636 eV and 0.632 to 0.720 eV for CF and FF
respectively, indicating the shallow electron traps. The
results also revealed that the PI for both of the fibres will
increase as the dose increase. The Ge-doped CF and FF
demonstrated a constant glow curves shape with
increasing dose. As the dose increases, area under the
glow curve increases, suggesting an increasing number of
electrons released from its traps.
Conclusion
CF demonstrated greater TL signal compared to FF. In
order to employ these optical fibres in absorbed dose
measurement, correction factors for energy dependence
and fading should be applied. The Ge-doped CF and FF
demonstrated the second-order kinetic model to the high
temperature half of the curve is slightly broader than the
low temperature half which suggest the possibility of
strong electron retrapping. The evaluation on Ge doped
optical fibres showed a highly favourable TL
characteristics exhibited by CF and FF indicate a great
potential in radiotherapy postal dose audit.
PO-0777 Importance of dosimetry formalism for cells
irradiation on a SARRP and consequences for RBE
M. Dos Santos
1
, V. Paget
2
, M. Ben Kacem
2
, F. Trompier
3
,
M. Benadjaoud
1
, A. François
2
, O. Guipaud
2
, M.
Benderitter
1
, F. Milliat
2
1
Institute for Radiobiological Protection and Nuclear
Safety IRSN, Department of Radiobiology and
Epidemiology SRBE, Fontenay-aux-Roses- Paris, France
2
Institute for Radiobiological Protection and Nuclear
Safety IRSN, Department of Radiobiology and
Epidemiology SRBE- Research on Radiobiology and
Radiopathology Laboratory L3R, Fontenay-aux-Roses-
Paris, France
3
Institute for Radiobiological Protection and Nuclear
Safety IRSN, Department of external dosimetry SDE-
Ionizing Radiation Dosimetry Laboratory LDRI, Fontenay-
aux-Roses- Paris, France
Purpose or Objective
Since last three decades, the importance of the dosimetry
in radiobiology studies and the standardization of the
dosimetry protocols have been highlighted. Nevertheless,
most of time, it is very difficult to reproduce experiments
described on literature due to a lack of details in the
description of dosimetry protocols. As the main objective
of radiobiology is to establish links between doses and the
radiations-induced biological effects, well-defined
dosimetry protocols appear to be a crucial point within the
determination of experimental protocols.
In this context, detailed dosimetry protocols for cells
irradiation have been implemented on the Small Animal
Radiation Research Platform (SARRP). To support the
importance of all parameters described on dosimetry
protocols, manual protocol changes were performed by
modifying the cell growth medium volume and/or the
additional filtration for an irradiation at 80 kV. Impacts of
modifications of the physical dose induced by these
errors/protocols changes were studied on RBE (Relative
Biological Effectiveness) using the survival clonogenic
assay.
Material and Methods
In first, all parameters of the configuration setup (HT, HVL
…) have to be defined. Then, measurements of absolute
dosimetry with ionization chamber calibrated in air Kerma
free in air condition, converted then in water kerma free
in air, and relative dosimetry with EBT3 radiochromic films
were performed to determine dose rate and evaluate the
attenuation due to the cell growth medium in each
containers
used
for
cells
irr
adiation.
In order to evaluate the influence of the modific ation of
parameters like cell medium volume (1 or 9 mL I nstead
of 3 mL as the reference condition) and/or the additional
filtration, 6 plate wells containing EBT3 films with water
were used to determine the impact on the physical dose
at 80 kV. Then, experiments with rigorously the same
irradiation conditions were performed by replacing EBT3
films by HUVECs. The biological response of HUVECs was
assessed by using clonogenic assay.
Results
Characterization of the beam quality index in the range of
30 to 220 kV for copper and aluminum filtrations and the
homogeneity of the field size have been measured.
Then, impact of the cell culture volume and filtration have
been evaluated thanks to measurements with EBT3 films
and show a variation between 1 to 8% with the copper
filtration and 8 to 40% with aluminum filtration compared
to each reference condition. HUVECs cells irradiated in
the same conditions showed significant differences in cell
survival fraction, perfectly corroborating the dosimetric
changes observed on physical dose.