822 / 1096
S806
ESTRO 36
_______________________________________________________________________________________________
Material and Methods
Brass bolus (Radiation Products Design Inc) with a nominal
thickness of 1.5mm was used on a tissue equivalent slab
phantom (RMI solid water). It was used as single layer and
folded over in 2 or 4 layers. Radiochromic film (EBT3) was
used to assess surface dose and dose variation on the
phantom for a 6 MV and 18MV photon beams (Varian 21iX).
Surface dose was measured with and without the brass
bolus which was placed on top of the film. A photo of the
brass is shown in Figure 1 (a) alongside a 50 mm section of
steel ruler. A film calibration curve was derived by
exposing samples from the same sheet to various known
doses under reference conditions. Film was scanned 12
hours post exposure and manually analysed using ImageJ
and MS Excel software.
Results
Surface dose measured using film in the absence of bolus
was 20 % of dose at d-max for a 6 MV beam in a 10 cm x
10 cm jaw-defined square field. Surface dose with a single
layer of the brass bolus increased to an average of 57 % of
dose at d-max (1.5cm). The mesh-like structure of the
brass resulted in a dose enhancement pattern which was
non-uniform across the film, as shown for a 1 cm x 1 cm
square region in Figure 1 (b), which shows the peaks and
troughs resulting from the mesh. The maximum dose
(peaks) was 62 % and the minimum (troughs) was 53 % of
dose at d-max under reference conditions. Increasing the
number of layers of bolus increased the surface dose.
Conclusion
Brass bolus may be used for surface dose enhancement in
external beam radiotherapy with megavoltage photons.
The surface dose increased from 20 % to 57 % of dose at d-
max for a 10 cm x 10 cm 6 MV field. The non-uniform
surface dose distribution should have minimal clinical
impact for multi-fraction radiotherapy regimes where
multiple layers and the random orientation of brass links
relative to skin surface will vary with daily setup.
EP-1503 The effect of tandem-ovoid applicator on the
dose distribution in GYN brachytherapy using Ir-192
M.H. Sadeghi
1
, A. Mehdizadeh
1
, M. Tafi
1
, R. Faghihi
1
, S.
Sina
2
, A.S. Meigooni
3
, A. Shabestani Monfared
4
1
Shiraz University, nuclear engineerning department,
Shiraz, Iran Islamic Republic of
2
Shiraz University, Radiation Research Center, Shiraz,
Iran Islamic Republic of
3
Comprehensive cancer center of Nevada, Las Vegas-
Nevada, USA
4
Babol University of Medical Sciences, Babol, Iran Islamic
Republic of
Purpose or Objective
The dosimetry procedures by simple superposition
accounts only for the source shield, and does not take in
to account the attenuation of photons by the applicators.
The purpose of this investigation is estimation of the
effects the tandem ovoid applicator on the dose
distribution inside the phantom by MCNP5 Monte Carlo
simulations.
Material and Methods
In this study, the superposition method is used for
obtaining the dose distribution in the phantom for a
typical GYN brachytherapy. Then the sources are
simulated inside the tandem ovoid applicator, and the
dose at points A, B, bladder and rectum was compared
with the results of supper position. The exact dwell
positions, and times of the source, and positions of the
dosimetry points were determined from images of a
patient. The MCNP5 Monte Carlo code was used for
simulation of the phantoms, applicators, and the sources.
Results
The results of this study showed no significant differences
between the results of superposition method, and the MC
simulations for different dosimetry points. The difference
in all important dosimetry points were found to be less
than 4%. The maximum dose differences were found at the
tip of the detectors.
Conclusion
According to the results, the superposition method, adding
the dose of each source obtained by the TG-43 algorithm,
can estimate the dose to point A, B, bladder,and rectum
points with good accuracy.
EP-1504 Monte Carlo modeling of non-isocentric proton
pencil beam scanning treatments
A. Elia
1,2
, L. Grevillot
1
, A. Carlino
1,3
, T. Böhlen
1
, H.
Fuchs
1,4,5
, M. Stock
1
, D. Sarrut
2
1
EBG MedAustron GmbH, Medical Department, A-2700
Wiener Neustadt, Austria
2
CREATIS- Université de Lyon- CNRS UMR5220- Inserm
U1044- INSA-Lyon- Université Lyon 1, Centre Léon
Bérard, 69007 Lyon, France
3
University of Palermo, Department of Physics and
Chemistry, 90128 Palermo, Italy
4
Medical University of Vienna / AKH, Department of
Radiation Oncology, Vienna, Austria
5
Medical University of Vienna, Christian Doppler
Laboratory for Medical Radiation Research for Radiation
Oncology, Vienna, Austria
Purpose or Objective
Monte Carlo (MC) calculation is the gold standard to
support dose calculation analytically performed by
Treatment Planning Systems (TPS). This work is built upon
a preliminary beam model of a fixed beam line based
mainly on measurements performed at isocenter. For non-
isocentric treatments, accurate description of beam spot
size for reduced air-gaps is of paramount importance for
accurate treatment planning. This work extends the