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S202
ESTRO 36 2017
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calculate the peak-to-peak amplitude of the respiration-
induced marker motion and the marker motion trajectory.
The mean and standard deviation (SD) of the peak-to-peak
amplitudes over the treatment course were compared
between the left-right (LR), cranial-caudal (CC), and
anterior-posterior (AP) directions; and between the
proximal, middle, distal esophagus, and proximal
stomach. Further, the SDs of the peak-to-peak amplitudes
and marker positions at the inhalation and exhalation
were calculated to assess the interfractional variability of
amplitude and trajectory shape. The correlation between
the mean peak-to-peak amplitude and these SDs was also
assessed.
Results
Overall, the mean and SD of the peak-to-peak amplitudes
were significantly larger in the CC than in the LR/AP
directions (median of mean[SD] in LR/CC/AP (mm):
2.0[0.6]/6.4[0.9]/2.4[0.7];
p
<0.05, Friedman with
Wilcoxon signed-rank test). It was also found to be
significantly larger for the distal esophagus
(2.6[0.6]/7.3[1.2]/3.1[0.7]) and proximal stomach
(2.2[0.9]/6.8[1.1]/4.2[1.1]) than for the proximal
(1.4[0.4]/2.7[0.7]/1.3[0.4])
and
middle
(1.6[0.5]/3.2[0.6]/1.6[0.5]) esophagus in all three
directions (Fig. 1;
p
<0.05, Kruskal-Wallis with Dunn’s
test). Moreover, the SDs of peak-to-peak amplitudes and
marker positions at the inhalation and exhalation were
≤2.1mm (median: ≤0.9mm) in all three directions,
suggesting a small interfractional variability of the motion
amplitude and a stable trajectory shape (Fig. 2). Further,
a weak correlation (coefficient R: 0.54–0.71,
p
<0.001) was
found between the mean peak-to-peak amplitude and the
interfractional variability of amplitude and trajectory
shape (Fig. 2), implying that in addition to the peak-to-
peak amplitude, other factors such as stomach fillings
could also influence the interfractional variability of
amplitude and trajectory shape.
Conclusion
The amplitude and variability of the respiration-induced
esophageal tumor motion were found to be dependent on
direction and region. The limited interfractional
variability suggests that using a single planning 4D-CT may
be sufficient to take into account the respiration-induced
esophageal tumor motion.