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ESTRO 36
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OC-0341 Monte Carlo dose calculations using different
dual energy CT scanners for proton range verification
I.P. Almeida
1
1
Maastricht Radiation Oncology MAASTRO clinic, Physics
Research, Maastricht, The Netherlands
Purpose or Objective
To simulate the dose profile for proton range verification
by means of Monte Carlo calculations and to quantify the
difference in dose using extracted values of relative
electron densities (
ρ
e
) and effective atomic numbers (
Z
eff
)
for three commercial dual-energy computed tomography
(DECT) scanners from the same vendor: a novel single-
source split-filter (i.e. twin-beam), a novel single-source
dual-spiral and a dual source device. This study aims also
to provide a comparison between the use of different
DECT modalities and the conventional single-energy CT
(SECT) technique in terms of dose distributions and proton
range.
Material and Methods
Measurements were made with three third generation
DECT scanners: a novel dual spiral at 80/140 kVp, a novel
twin-beam at 120 kVp with gold and tin filters, and a dual-
source scanner at 90/150kVp with tin filtration in the high
energy tube. Images were acquired with equivalent CTDI
vol
of approximately 20 mGy and reconstructed with
equivalent iterative reconstruction algorithms. Two
phantoms with tissue mimicking inserts were used for
calibration and validation. Monte Carlo proton dose
calculations were performed with GEANT4, in which the
materials and densities were assigned using the DECT
extracted values of
ρ
e
and
Z
eff
for both phantoms.
Simulations were done with monoenergetic proton beams
impinging under directions to the cylindrical phantoms,
covering different tissue-equivalent inserts. Dose
calculations were also performed on images from a third
generation SECT scanner at 120 kVp. Simulations based on
DECT and SECT images were compared to a reference
phantom.
Results
Range shifts on the 80% distal dose fall-off (R80) were
quantified and compared for the different beam directions
and media involved to a reference phantom. Maximum R80
range shifts from the reference values for the calibration
phantoms based on DECT images were 3.5 mm for the
twin-beam, 2.1 mm for the dual-spiral and for the dual-
source. For the same phantom, simulations based on SECT
images had a maximum range shift of 4.9 mm. 2D stopping
power maps were computed and compared for the
different techniques.
Figure 1. Illustration of the beam 1 direction in the
calibration phantom with different tissue-equivalent
inserts.
Figure 2: Dose to water profile for one beam direction in
the Gammex RMI 467 phantom. The dose is laterally
integrated and the R80 is measured.
Conclusion
A comparison study between the use of SECT and DECT
images for proton dose distribution is performed to
understand the differences and potential benefit of DECT
for proton therapy treatment planning, using different CT
scanners. The final aim is to decrease uncertainty in dose
delivery, possibly allowing narrower treatment margin
than currently used. In most scenarios, the different
modalities of DECT produced results closer to the
reference, when compared with the SECT based
simulations. Small differences were found for the
different DECT scanners.
OC-0342 Monte Carlo simulations of a low energy
proton beam and estimation of LET distributions
T.J. Dahle
1
, A.M. Rykkelid
2
, C.H. Stokkevåg
3
, A. Görgen
2
,
N.J. Edin
2
, E. Malinen
2,4
, K.S. Ytre-Hauge
1
1
University of Bergen, Department of Physics and
Technology, Bergen, Norway
2
University of Oslo, Department of Physics, Oslo, Norway
3
Haukeland University Hospital, Department of Oncology
and Medical Physics, Bergen, Norway
4
Oslo University Hospital, Department of Medical
Physics, Oslo, Norway
Purpose or Objective
The physical advantage of protons in radiotherapy is
mainly due to the ‘Bragg peak’ of the proton depth dose
distribution. However, there is still a controversy on the
biological effects of protons, in particular around the
Bragg peak. This relates both to the variability of