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phantom consisting of (20)3 μm3 voxels). Microscopic extension probability (MEP) models were
developed using Matlab-2012a, based on the function fitted to clinical studies reporting on recurrence
patterns of GBM. Three MEP patterns were considered: isotropic (Circular) and anisotropic (Elliptical and
Irregular). The results of microdosimetry model and MEP models were convolved to evaluate survival
fractions (SF) for CTV margins of 2 and 2.5 cm. additionally, hypoxia and genetic heterogeneity profiles
were incorporated into the MEP model and the effect of CTV margin extension on SFs was investigated.
The heterogeneity was modelled using a range of α/β values associated with different GBM cell lines.
These values were distributed among the cells randomly, taken from a Gaussian-weighted sample of α/β
values. Likewise, hypoxia was distributed randomly taken from a sample weighted to the intratumoural
and peritumoural oxygen profiles obtained from literature. Results: The improvement in SF as a result of
CTV extension was calculated for all MEP models and was found to be the lowest for circular MEP model:
72.37, 73.09, and 72.31%, and highest for elliptical MEP model: 77.74, 78.56, and 77.76% for
homogeneous-normoxic, heterogeneous-normoxic, and heterogeneous-hypoxic, respectively.
Introduction of heterogeneity and hypoxia, despite being very extensive in GBM, had little effect on total
SF reduction due to CTV extension. The survival within the beam, however, was increased markedly for
heterogeneous hypoxic GBM. Conclusion: MC model was developed to quantitatively evaluate the impact
of GBM CTV margin on SF. The results suggest that there is approximately an order of magnitude reduction
in survival fraction when CTV is extended by 0.5 cm. The total SF is affected mostly by the presence of
clonogens in the penumbra region and to a lesser extent by heterogeneity and hypoxia (which primarily
affect the in-beam survival).
1;2
(PS5-17) Comparison of electron track structure in water and DNA medium. Marion U. Bug ; Woonyong
1
1
1
Baek ; and Hans Rabus , Physikalisch-Technische Bundesanstalt, Braunschweig, Germany and University
of Wollongong, Wollongong, Australia
2
DNA damage caused by densely ionizing radiation is conventionally estimated from simulated
parameters of the particle track structure. These track structure simulations require the implementation
of cross section data for the interaction of the incident particles and their secondaries with molecules of
the medium. Liquid water is conventionally used to represent biological matter, as cross section data of
DNA constituents were previously fragmentary. Hence, an influence of the difference in cross section data
on simulated track structure parameters could not have been investigated. We present the evaluation of
a complete set of interaction cross sections of DNA constituents for impact of electrons with energies
between 6 eV and 1 keV. These new data are based on measurements of total scattering cross sections
[1, 2], differential elastic scattering cross sections [1] and double-differential ionization cross sections of
tetrahydrofuran, pyrimidine and trimethylphosphate. The evaluated cross section data set was
implemented in the Monte Carlo code PTra [3] to simulate electron track structure in DNA medium. The
particle track structure is generally characterized by nanodosimetric quantities, such as the probability
distribution of ionization cluster size [3] (i.e. number of ionizations produced per primary particle within
a nanometric volume). Nanodosimetric quantities were calculated by simulations of electrons with
energies below 1 keV in water and DNA medium. The differences in the results obtained in the different
media are discussed. [1] W.Y. Baek et al., Phys. Rev. A 86, 032702 (2012). [2] W.Y. Baek et al., Phys. Rev.
A 88, 032702 (2013). [3] B. Grosswendt, Radiat. Prot. Dosim. 110, 789 (2004).
294 | P a g e
developed using Matlab-2012a, based on the function fitted to clinical studies reporting on recurrence
patterns of GBM. Three MEP patterns were considered: isotropic (Circular) and anisotropic (Elliptical and
Irregular). The results of microdosimetry model and MEP models were convolved to evaluate survival
fractions (SF) for CTV margins of 2 and 2.5 cm. additionally, hypoxia and genetic heterogeneity profiles
were incorporated into the MEP model and the effect of CTV margin extension on SFs was investigated.
The heterogeneity was modelled using a range of α/β values associated with different GBM cell lines.
These values were distributed among the cells randomly, taken from a Gaussian-weighted sample of α/β
values. Likewise, hypoxia was distributed randomly taken from a sample weighted to the intratumoural
and peritumoural oxygen profiles obtained from literature. Results: The improvement in SF as a result of
CTV extension was calculated for all MEP models and was found to be the lowest for circular MEP model:
72.37, 73.09, and 72.31%, and highest for elliptical MEP model: 77.74, 78.56, and 77.76% for
homogeneous-normoxic, heterogeneous-normoxic, and heterogeneous-hypoxic, respectively.
Introduction of heterogeneity and hypoxia, despite being very extensive in GBM, had little effect on total
SF reduction due to CTV extension. The survival within the beam, however, was increased markedly for
heterogeneous hypoxic GBM. Conclusion: MC model was developed to quantitatively evaluate the impact
of GBM CTV margin on SF. The results suggest that there is approximately an order of magnitude reduction
in survival fraction when CTV is extended by 0.5 cm. The total SF is affected mostly by the presence of
clonogens in the penumbra region and to a lesser extent by heterogeneity and hypoxia (which primarily
affect the in-beam survival).
1;2
(PS5-17) Comparison of electron track structure in water and DNA medium. Marion U. Bug ; Woonyong
1
1
1
Baek ; and Hans Rabus , Physikalisch-Technische Bundesanstalt, Braunschweig, Germany and University
of Wollongong, Wollongong, Australia
2
DNA damage caused by densely ionizing radiation is conventionally estimated from simulated
parameters of the particle track structure. These track structure simulations require the implementation
of cross section data for the interaction of the incident particles and their secondaries with molecules of
the medium. Liquid water is conventionally used to represent biological matter, as cross section data of
DNA constituents were previously fragmentary. Hence, an influence of the difference in cross section data
on simulated track structure parameters could not have been investigated. We present the evaluation of
a complete set of interaction cross sections of DNA constituents for impact of electrons with energies
between 6 eV and 1 keV. These new data are based on measurements of total scattering cross sections
[1, 2], differential elastic scattering cross sections [1] and double-differential ionization cross sections of
tetrahydrofuran, pyrimidine and trimethylphosphate. The evaluated cross section data set was
implemented in the Monte Carlo code PTra [3] to simulate electron track structure in DNA medium. The
particle track structure is generally characterized by nanodosimetric quantities, such as the probability
distribution of ionization cluster size [3] (i.e. number of ionizations produced per primary particle within
a nanometric volume). Nanodosimetric quantities were calculated by simulations of electrons with
energies below 1 keV in water and DNA medium. The differences in the results obtained in the different
media are discussed. [1] W.Y. Baek et al., Phys. Rev. A 86, 032702 (2012). [2] W.Y. Baek et al., Phys. Rev.
A 88, 032702 (2013). [3] B. Grosswendt, Radiat. Prot. Dosim. 110, 789 (2004).
294 | P a g e
