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the competing events of cell mutation and inactivation.
The RBE variation for the different end-points was
included by introducing and varying the ratio (k) between
cell mutation and inactivation for C-ions. The median and
range of the patient-specific RRs were calculated from the
physical dose distributions and the published input model
parameters.
Results
The dose distributions (Fig 1) illustrated the sharper
lateral penumbra of C-ions, which resulted in lower lung
doses compared to protons, while the C-ion fragmentation
tail contributed to higher doses to the thyroid than from
protons. The SC risk estimates strongly depended on the
ratio k, and the RR decreased for increasing k for both
organs (Fig 2). For the thyroid, the RR was higher from the
C-ion plans for the entire scanned range of k. Despite a
better sparing of the lungs with C-ions, the carcinogenic
potential of C-ions was not consistently lower than for
protons: Not including a difference in end-point resulted
in RRs in favour of C-ions, while increasing the ratio k gave
higher risks for C-ions compared to protons. For the lungs,
the median RR turned in favour of IMPT at a threshold
value
k=1.1.
Conclusion
Varying the RBE depending on end-point may strongly
influence results when estimating carcinogenic risks from
C-ion therapy and should be included in modelling risk of
radiation-induced SC from C-ion therapy.
EP-1608 Deriving HPV status from standard CT imaging:
a radiomic approach with independent validation
R. Leijenaar
1
, M. Nesteruk
2
, G. Feliciani
1
, F. Hoebers
1
, J.
Van Timmeren
1
, W. Van Elmpt
1
, S. Walsh
1
, A. Jochems
1
,
S. Huang
3
, B. Chan
3
, J. Waldron
3
, B. O'Sullivan
3
, D.
Rietveld
4
, C. Leemans
5
, O. Riesterer
2
, K. Ikenberg
6
, P.
Lambin
1
1
MAASTRO Clinic, Department of Radiation Oncology-
GROW- School for Oncology and Developmental Biology-
Maastricht University Medical Centre, Maastricht, The
Netherlands
2
University Hospital Zurich and University of Zurich,
Department of Radiation Oncology, Zurich, Switzerland