427 / 1096
S412
ESTRO 36
_______________________________________________________________________________________________
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.
Conclusion
All together these results strongly support the fact that an
accurate dosimetry needs to be performed before an
experiment but also to cautiously follow all the defined
parameters for one condition of irradiation to avoid errors
in the dose delivered on the sample and to be able to
properly compare and interpret experiments.
PO-0778 New Razor silicon diode for Cyber Knife small
beam relative dosimetry: a multi-site evaluation
S. Russo
1
, L. Masi
2
, P.R. Dicarolo
3
, R. Doro
2
, E. De
Martin
4
, M.L. Fumagalli
4
, A.S. Martinotti
5
, A. Bergantin
5
,
E. Rondi
6
, S. Vigorito
6
, P. Mancosu
7
1
Aziend USL Toscana Centro, Fisica Sanitaria, Florence,
Italy
2
IFCA, Radiotherapy, Firenze, Italy
3
Medical Physycs, Meyer Children’s University Hospital-,
Florence, Italy
4
Istituto Besta, Radiotherapy, Milano, Italy
5
C.D.I., Radiotherapy, Milano, Italy
6
I. E. O., Radiotherapy, Milano, Italy
7
Humanitas Research Hospital, Medical Physics Unit of
Radiation Oncology, Milan, Italy
Purpose or Objective
The aim of this work was to evaluate the suitability of a
new unshielded p-type silicon diode (Razor, IBA
Dosimetry, Germany) for relative small beams dosimetry
over different CyberKnife systems.
Material and Methods
Output Factors
(OFs) measurements with Razor detector
were performed by four Italian Radiotherapy Centers
equipped with CyberKnife units for field sizes ranging from
5 to 60 mm, defined by fixed circular collimators. Setup
conditions were 80 cm source to detector distance and 1.5
cm depth in water. Measurements were repeated by each
center with a PTW-60017 diode. Monte Carlo correction
factors reported in literature were applied to PTW-60017
measured data and corrected values were considered as a
reference.
Crossplane and inplane dose profiles ranging from 5-60 cm
fixed collimators were measured by Razor detector at a
depth of 10 cm in water and SSD 70 cm. The effective field
size (EFS), defined as EFS=, where A and B correspond to
the in- and cross-line FWHM, were calculated. Penumbra
20%- 80% was also evaluated.
This work has been conducted in the framework of the
Italian Association of Medical Physics (AIFM) SBRT working
group.
Results
Razor OFs measured for fixed collimators in the four
enrolled centers showed a variability (relative range)
decreasing from 1.2% to 0.4% for field sizes from 7.5 to 60
mm and equal to 2.2% for the smallest cone. The
variability obtained for OF measured by PTW-60017 was
analogous: lower than 1 % for field sizes from 7.5 to 60
mm and equal to 3.5% for the smallest diameter.
For field sizes down to 7.5 mm Razor measured OFs were
lower than PTW-60017 uncorrected measured values.
Relative differences between Razor OFs and Monte Carlo
corrected PTW-60017 data were below 1% for 60-10 mm
cone sizes and within 2 % for 7.5 mm field size over all
centers. For the smallest collimator differences ranging
from to 2.5% to 6% were observed among centers. Average
values and SD of OFs measured by Razor and PTW-60017
diode (MC corrected and not) are shown in figure.
Nominal field size NFS, effective field size EFS and
penumbra Razor measurements averaged over the four
CyberKnife centers are reported in table. Maximum