ESTRO 36 Abstract Book

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S149 ESTRO 36
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PV-0284 3D Performance Analysis of Cyberknife
Synchrony® Respiratory Tracking System
M.C. Sahin1, P. Hurmuz1, M. Yeginer1, G. Yazici1, G.
Ozyigit 1
1 Hacettepe University Faculty of Medicine, Radiation
Oncology, Ankara, Turkey
Purpose or Objective
Tumor movement is a challenging issue for the precise
delivery of radiation for thoracic tumors. The Synchrony
respiratory motion tracking system (RMTS) of Cyberknife®
robotic radiosurgery unit synchronizes radiation beam
delivery with the respiration induced tumor motion. This
study aims to investigate the performance of Synchrony
RMTS for different movement widths using polymer gel
dosimetry. To the best of our knowledge this is the first
study to make the three dimensional performance analysis
of Synchrony RMTS.
Material and Methods
The MultiPlan® treatment planning system (TPS) of
Cyberknife® was used to deliver 4 Gy to a tumor of 1X1X1
cm 3. BrainLab Gating lung phantom was used to simulate
lung movements with three different amplitudes (1 cm, 2
cm and 3 cm). Three fiducials were inserted to the
phantom for tracking. Radiochromic film and polymer gel
dosimetry were used and measurements were compared
with the dose distributions acquired from the TPS. The
dose information of irradiated gel were read out using 1.5
T magnetic resonance imaging. The gamma index values
were analysed using the Ashland FilmQA Pro 3.0 software
for film dosimeters and Polygevero software for gel
dosimeters using the 3mm/3% criteria. PolyGevero gamma
index value of ≤1 is accepted as a passing criteria
according to the literature.
Results
The mean 3 mm/3% gamma index values of film dosimetry
were 92.6±1.94%, 91.0±4.00%, 90.3±2.04% for tumor
motions of 1 cm, 2 cm and 3 cm, respectively
(p<0.001). For polymer gel dosimetry, the mean gamma
index values calculated over almost three million points
were 0.56±0.10, 0.60±0.24 and 0.65±0.30 for tumor
motions of 1 cm, 2 cm and 3 cm, respectively (p<0.001).
Although the difference was statistically significant for 3
different amplitudes, the performance of the system was
within the acceptance limits
(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 Merkelsen1, B. Roche 1, J.P.
Bangsgaard1
1Rigshospitalet, 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).