260 / 1096
S247
ESTRO 36
_______________________________________________________________________________________________
were associated with increased mortality, recurrence and
disease progression in chemo-radiated patients with
advanced tumours in our cohort (shown in figure) and with
survival in the TCGA HNSCC cohort.
Conclusion
We developed a model that exposes DNA repair defects
as it predicts hypersensitivity to DNA crosslinking agents
caused by such defects
in vitro
. The model successfully
predicted sensitivity in an independent dataset. We found
that increased probabilities of DNA repair defects were
associated with poorer outcome in patients, possibly a
result of the impact on genomic instability.
Proffered Papers: Highlights of proffered papers
OC-0464 Validation of a fully automatic real-time liver
motion monitoring method on a conventional linac
J. Bertholet
1
, R. Hansen
1
, E.S. Worm
1
, J. Toftegaard
1
, H.
Wan
2
, P.J. Parikh
2
, M. Høyer
1
, P.R. Poulsen
1
1
Aarhus University Hospital, Department of oncology,
Aarhus C, Denmark
2
Washington University- School of Medicine, Department
of Radiation Oncology, St-Louis, USA
Purpose or Objective
Intrafraction motion is a challenge for accurate liver
radiotherapy delivery. Real-time treatment adaptation
(gating, tracking) may mitigate the detrimental effects of
motion, but requires reliable target motion monitoring. In
this study, we develop and validate a framework for fully
automatic monitoring of thoracic and abdominal tumors
on a conventional linac by combining real-time marker
segmentation in kV images with internal position
estimation by an external correlation model (ECM). The
validation is based on experiments and simulations using
known external and internal motion for 10 liver SBRT
patients.
Material and Methods
A fully automatic real-time motion monitoring framework
was developed. The framework combines auto-
segmentation of arbitrarily shaped implanted fiducial
markers in CBCT projections and intra-treatment kV
images with simultaneous streaming of an external optical
motion signal. Fig. A illustrates the workflow: A pre-
treatment CBCT is acquired with simultaneous recording
of the motion of an external block on the abdomen. The
markers are segmented in every CBCT projection and a 3D
voxel model of each marker is generated. The 3D marker
motion is estimated from the observed 2D motion and used
to optimize an ECM of the 3D internal marker motion
INT(t) as a function of the external motion EXT(t). During
treatment, INT(t) is estimated from EXT(t) at 20Hz, while
MV-scatter-free kV images are acquired every 3s during
beam pauses. The markers are segmented in real-time
using the ECM to determine the search area and
projections of the 3D voxel model as templates. The ECM
is continuously updated with the latest estimated 3D
marker position. The method was validated using Calypso-
recorded internal motion and simultaneous camera-
recorded external motion of 10 liver SBRT patients. The
validation included both experiments with a
programmable motion stage and simulations hereof for the
first patient as well as simulations for the remaining
patients. The real-time estimated 3D motion was
compared to the known tumor motion. For comparison,
the position estimation error was also calculated without
ECM updates.
Results
The segmentation rate was 90% with a mean 2D
segmentation error of 1.5pixels. Fig. B compares the
estimated and actual target motion for a portion of the
phantom experiment for Patient 1. The simulations agreed
with the experimental root-mean-square error within
0.4mm (Table 1). For all patients, the mean 3D root-mean-
square error was 1.74mm with ECM updates and 2.47mm
without ECM updates (Table 1).
Conclusion
A real-time 3D tumor motion monitoring method was
established and validated in experiments and simulations
using known Calypso-recorded liver tumor motion. The
method is fully automatic and can be used for arbitrarily
shaped fiducial markers in the thorax or abdomen on a
conventional linac without additional time or hardware.
The internal position estimation can also be performed for
non-coplanar fields where there is no room to deploy the
kV imaging system.