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Figure 1: ROC curves of the model validation.
Conclusion
The combination of deep learning and radiomics features
has similar performance to conventional radiomics
modelling strategies. However, feature selection is no
longer a required component as all features can be
included in the network. This is a major advantage as
feature selection is a computationally intractable task for
which only heuristic solutions exist.
References
1 Aerts, H. et al,
Nat. Commun.
2014
,
5
, 4006.
EP-1606 Calculating ion-induced cell death and
chromosome damage by the BIANCA biophysical model
M.P. Carante
1,2
, F. Ballarini
1,2
1
Istituto Nazionale di Fisica Nucleare INFN, Section of
Pavia, Pavia, Italy
2
University of Pavia, Physics Department, Pavia, Italy
Purpose or Objective
To calculate probabilities of cell death and chromosome
aberrations following cell irradiation with ion beams of
different energy.
Material and Methods
A biophysical model called BIANCA (BIophysical ANalysis of
Cell death and chromosome Aberrations) [Carante M.P.
and Ballarini F.
Front. Oncol.
6:76 2016] was refined and
applied to simulate cell death and chromosome
aberrations by therapeutic protons and heavier ions. The
model, which assumes a pivotal role for DNA cluster
damage, is based on the following assumptions: i) a DNA
“Cluster Lesion” (CL) produces two independent
chromosome fragments; ii) chromosome fragment un-
rejoining, or distance-dependent mis-rejoining
,
gives rise
to chromosome aberrations; iii) certain aberrations
(dicentrics, rings and large deletions) lead to cell death.
The CL yield is an adjustable parameter, as well as the
probability that a chromosome fragment remains un-
rejoined even if possible partners for rejoining are
present. The model, implemented as a MC code providing
simulated dose-response curves comparable with
experimental data, was applied to different beams,
including beams available at the CNAO hadrontherapy
centre in Pavia, Italy, and at the CATANA facility in
Catania, Italy.
Results
The model allowed reproduction of experimental survival
curves for cell lines characterized by different
radiosensitivity, supporting the model assumptions.
Furthermore, cell death and chromosome aberrations
along SOBP dose profiles were predicted also for depth
positions where experimental data were not available. A
formula was also derived to predict cell death and
chromosome damage for a different cell line exposed to a
given ion type and energy, basing on the response of a
reference cell line to the same radiation quality. For both
endpoints, the increase of effectiveness along the plateau
was quantified. A non-negligible increase was found also
for protons, associated to high levels of damage beyond
the distal dose fall-off, due to the lower energy and thus
the higher biological effectiveness.
Conclusion
In line with other studies, this work suggests that assuming
a constant RBE along a proton SOBP may be sub-optimal.
More generally, this work represents an example of
therapeutic beam characterization avoiding the use of
experimental RBE values, which can be source of
uncertainties.
Acknowledgements:
this work was partially supported by
INFN (project ETHICS, P.I. L. Manti, local P.I. F. Ballarini;
MC-INFN/FLUKA, P.I. P. Sala, local P.I. A. Fontana)
EP-1607 Secondary cancer risk after particle therapy
for organs distal or lateral to the target volume
L. Toussaint
1
, L. Muren
1
, G. Engeseth
2
, C. Stokkevåg
2
1
Aarhus University Hospital, Medical Physics, Aarhus C,
Denmark
2
Haukeland University Hospital, Department of Oncology
and Medical Physics, Bergen, Norway
Purpose or Objective
Proton therapy is the most used particle therapy modality,
but carbon ions are also increasingly being applied for
specific tumour entities. Particle therapy in general has a
known potential of reducing the irradiated volumes of
normal tissues, although protons and carbon ions have
distinctively different dose distribution characteristics.
Protons have a steeper dose fall-off distally while carbon
ions have a sharper lateral dose penumbra. In addition,
carbon ions have a higher biological effect due to
increased cell inactivation, but also for the end-point cell
mutation associated with carcinogenic potential. The aim
of this study was therefore to compare the risk of
secondary cancer (SC) from dose distributions in the
thyroid and lungs, particularly radiosensitive organs
located distally and laterally to the target volume during
craniospinal irradiation (CSI). Since pre-clinical data
indicates that the carbon ions RBE for cell mutation may
be higher than for cell inactivation, we included this in the
models.
Material and Methods
CSI treatment plans with a prescribed dose of 23.4Gy(RBE)
were generated on CT-scans from six pediatric patients
(Syngo, Siemens) using pencil beam scanning protons
(IMPT) and carbon ions (C-ions). Relative risks (RRs) of
radiation induced cancer (IMPT/C-ions) for the thyroid and
the lungs were analysed by applying a bell-shaped dose-
response model (J Radiol Prot 2009; 29(2A): A143-157).
The model accounts for RBE, fractionation as well as for