ESTRO 36 Abstract Book

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S863 ESTRO 36 2017
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start of treatment and to monitor deviations during
treatment.
An in-house developed real-time automated monitoring
system of the respiratory motion is implemented to verify
the reproducibility and stability of the vmDIBH during
breast cancer treatments.
Material and Methods
Patients with left sided breast cancer are guided to
perform vmDIBH assisted by verbal instructions and an
additional aid called the ‘breathing stick’ [1].
A 3D Kinect v2 camera (Microsoft, USA) was mounted in
the treatment room to visualize the patient on the
treatment couch. Software was developed to track and
visualize the anterior–posterior motion of a small area of
the surface of the thoracic wall in real time, allowing RTTs
in the treatment room to verify the reproducibility and
stability of the breath holds during treatment.
The data of ten patients was analysed for reproducibility
and stability. The formulas for reproducibility and stability
were derived from Cerviño et al. with minor adaptations
[2]. For reproducibility the standard deviation of the mean
of each DIBH level was used. For stability all breath holds
were fitted by first order polynomials, the slopes were
multiplied by their breath hold lengths to find a range and
all these ranges were averaged.
Results
A typical example of reproducible and stable vmDIBHs
during a treatment fraction of a patient is shown in Figure
1.
Figure 1: Typical example of five reproducible and stable
vmDIBHs for one treatment fraction
The analysed reproducibility and stability of vmDIBH
treatment for then patients using the breathing stick is
shown in Figure 2. The median reproducibility and stability
were 0.9 mm and 1.1 mm, respectively.
Figure 2: Clinical measurements of the reproducibility and
stability of the vmDIBHs for ten patients
Conclusion
The reproducibility and stability of the chest wall can be
accurately measured using the in- house developed
monitoring system. vmDIBH in combination with the
breathing stick shows good stability and reproducibility
which are comparable to the results in the study of
Cerviño et al. [2].
In this work the current results are limited to ten patients;
we continue to, acquire more data for future analyses.
The breathing stick is routinely used in our clinic;
currently we use the breath hold monitoring system to test
whether using this tool has an added value.
References
[1] Brouwers PJ et al. Set-up verification and 2-
dimensional electronic portal imaging device dosimetry
during breath hold compared with free breathing in breast
cancer radiation therapy. Pract Radiat Oncol. 2015 May-
Jun;5(3):e135-41
[2] Cerviño L et al. Using surface imaging and visual
coaching to improve the reproducibility and stability of
deep-inspiration breath hold for left-breast-cancer
radiotherapy. Phys. Med. Biol. 54 (2009) 6853–6865
EP-1618 Can diaphragm motion function as a surrogate
for motion of esophageal tumors during treatment?
S.E. Heethuis1, L. Goense1, A.S. Borggreve1, P.S.N. Van
Rossum1, R. Van Hillegersberg2, J.P. Ruurda2, S. Mook1,
G.J. Meijer1, J.J.W. Lagendijk1, A.L.H.M.W. Van Lier1
1University Medical Center Utrecht, Department of
Radiotherapy, Amsterdam, The Netherlands
2University Medical Center Utrecht, Department of
Surgery, Amsterdam, The Netherlands
Purpose or Objective
Esophageal tumors show large motion in cranio-caudal
direction (CC), with a Peak-to-Peak (P-t-P) range of 2.7 to
24.5mm [Lever F. et al. (2013)]. In case the motion of the
tumor could be followed during radiotherapy treatment,
this would enable treatment margin reduction. The aim of
this research is to investigate whether the motion of the
diaphragm is correlated with breathing motion and drift
we can detect in esophageal tumors. As such, the
diaphragm could function as a surrogate for esophageal
tumor motion during treatment.
Material and Methods
In total, 46 coronal cine MR scans were obtained from 4
patients whom were treated with neoadjuvant
chemoradiotherapy (nCRT) for distal esophageal cancer.
In this study, one MR scan was performed prior to nCRT,
followed by 5 weekly MR scans during nCRT (in one patient
only 4 scans). Cine MR scans included 75 frames acquired
in approximately 45 seconds, with a resolution of
2.01x2.01mm. The scan was acquired twice within one
session, separated by circa 10 minutes. To estimate
motion in the cine MR series an optical flow algorithm
(RealTITracker, [Zachiu C. et al. (2015)]) was used to
calculate motion fields. The tumor was delineated
manually, in which the mean motion for each frame was
calculated in CC direction. Motion was also estimated in
the diaphragm/liver border within a manually placed
rectangle. An in-house tool was designed to find peaks and
estimate drifts in the motion curves. Drift was defined as
the change in the mean between consecutively found local
maxima and minima. Correlation of the CC motion
between diaphragm and tumor was calculated. P-t-P
analysis was performed on tumor motion curves and tumor
motion curves corrected for drift using the diaphragm drift
(Fig. 1).
Results
A strong Pearson’s correlation of r=0.972 was found while
comparing CC motion in diaphragm and tumor, with a
range of 0.849-0.996. The mean P-t-P tumor motion
before and after correction for drift was 10.1 and 9.3mm
respectively (p<0.05). However, for individual scan
sessions the effect of drift could be much larger, as is
exemplified in Fig. 1a. P-t-P amplitude for each patient
before and after drift correction is shown in Fig. 2 .
Although the amplitude of the diaphragm motion was
higher, mean P-t-P motion of 12.6mm, when the tumor
motion showed a drift or sudden movement, this was also
found in the diaphragm motion (Fig. 1&2).
Conclusion
In this study it was found that diaphragm motion shows a
strong correlation with esophageal tumor motion. Using
the diaphragm motion for drift correction resulted on
average in a reduction of the P-t-P range over all patients.
This reduction can be used for adaptive treatment
strategies, which reduce margins. For example, in case an
MR-linac is taken in mind [Lagendijk J.J.W. et al (2008)],
MR-based gating to compensate for respiratory motion
and/or base-line shift (drifting) detection using the
diaphragm as surrogate will be well feasible.