ESTRO 36 Abstract Book

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S148 ESTRO 36 2017
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(Figure1).
Conclusion
Three dimensional performance analysis showed that
Cyberknife Synchrony® RMTS is successful in tumor
tracking regardless of the amplitude of movement.
This study is supported by TUBITAK 3001 project, project
number 115S446
PV-0285 Using a surface scanner for positioning of
pelvic patients - can X-ray images be omitted?
J.B. Thomsen1, S. B.N. Biancardo1, S.H. Hattel1, L.
Søndergaard Vinther Merkelsen 1, B. Roche1, J.P.
Bangsgaard1
1 Rigshospitalet, Finsenscentret- Radiotherapy,
Copenhagen, Denmark
Purpose or Objective
Reproducing the correct treatment position prior to
radiotherapy is crucial for accurate dose delivery. The
golden standard for positioning is X-ray based imaging with
the drawback of exposing the patient to ionising radiation.
More recently surface scanners using infrared light has
been introduced to monitor the patient surface. We
investigate a surface monitor system ”AlignRT” for
positioning pelvic patients prior radiotherapy [Vision RT,
]. This is attractive in terms of saving
time and reducing imaging dose to the patient. Even when
acquiring daily X-ray images routinely, the ability to
correct rotations using AlignRT is of value to limit
repeated X-ray images.
Material and Methods
Patients undergoing pelvic irradiation were positioned
using the surface scanner. The body surface was extracted
from the CT therapy scan acquired before radiotherapy
and imported in the surface scanner software. With the
patient on the couch it is possible to monitor the surface
in the treatment region and the system displays the
deviations from the CT therapy scan translational and
rotational. We chose a region of interest (ROI) around the
treatment region of about 20 cm in cranio-caudal direction
and extending on both sides of the patient. Following
positioning using the surface scanner, a cone-beam CT
scan (CBCT) was acquired which makes a comparison
between the positioning using the surface scanner and the
CBCT possible. For the CBCT an automatic bone match was
applied using commercial software (Varian inc., offline
review) and visually inspected. In total, 105 fractions from
6 patients were analyzed and a paired T-test was applied
to detect any significant differences between the two
systems.
Results
In 50 of 105 fractions (48%) the difference between the
two positioning procedures was larger than 5 mm in at
least one direction. In 39 of 78 fractions (37%) the
difference in rotations was larger than 3 degrees . In 71 of
105 fractions (68%) either a difference in translations was
above 5mm or rotation above 3 degrees. In fig. 1 and fig.
2 the difference in translations and rotations are shown
for all 105 fractions originating from 6 patients. For the
translation there was a significant difference for vertical
and longitudinal directions (P<0,001 for vertical, P<0,001
for longitudinal, P<0,9 for lateral). The difference in
rotations were all significant (P<0,001 for pitch, P<0,05
for roll, P<0,01 for rotation around the vertical axis).
Conclusion
We did show significant deviations between positioning
using the surface scanner and CBCT with the chosen ROI.
In this small patient cohort, 68% of the fractions would
have been out of tolerance using a threshold of 5mm and
3 degrees if positioned solely based on the surface
scanner. Therefore a surface scanner does not replace the
usual X-ray image guidance procedure. Furthermore, for
pelvic patients it does not seem possible to use the surface
scanner for reliable estimations of rotational deviations
which could have limited repeated x-ray imaging.
PV-0286 Quantifying registration uncertainties in
image-based data mining
E.M. Vasquez Osorio1, A. McWilliam1,2, J. Kennedy3, C.
Faivre-Finn1,4, M. Van Herk1,2
1The University of Manchester, Division of Molecular &
Clinical Cancer Studies- School of Medical Sciences-
Faculty of Biology- Medicine and Health, Manchester,
United Kingdom
2The Christie NHS Foundation Trust, Christie Medical
Physics and Engineering, Manchester, United Kingdom
3The Christie NHS Foundation Trust, Informatics,
Manchester, United Kingdom
4The Christie NHS Foundation Trust, Clinical Oncology,
Manchester, United Kingdom
Purpose or Objective
Image based data mining relies on non-rigid registration to
bring image data on a common frame of reference.
Registration uncertainties will affect the analysis and must
be quantified and incorporated. We have developed a
method to quantify global and local random registration
uncertainties. Additionally, we evaluated the impact of
accounting for global random registration uncertainties on
the results of a recent lung data mining study that
identified the base of the heart as a dose sensitive region
affecting survival in lung cancer patients [1].
Material and Methods