Highlights
- •For dynamic tumor tracking, the accuracy of the correlation model between internal and external motion is a key issue.
- •To construct a correlation model, the internal and external motions are monitored for several tens of seconds.
- •We assessed the utility of 10 s and 20 s modeling periods, rather than the 40 s currently used, in the clinical practice.
- •The accuracies of correlation models derived using 20 s were almost identical to those obtained over 40 s.
- •The accuracies of correlation models derived using 10 s was reduced compared with those obtained over 20 s.
Abstract
Purpose
To assess the utility of 10 s and 20 s modeling periods, rather than the 40 s currently
used, in the clinical construction of practical correlation models (CMs) in dynamic
tumor tracking irradiation using the Vero4DRT.
Methods
The CMs with five independent parameters (CM parameters) were analyzed retrospectively
for 10 consecutive lung cancer patients. CM remodeling was performed two or three
times per treatment session. Three different CMs trained over modeling periods of
10, 20, and 40 s were built from a single, original CM log file. The predicted target
positions were calculated from the CM parameters and the vertical displacement of
infrared markers on the abdomen (PIR) during the modeling. We assessed how the CM parameters obtained over modeling periods
of T s (T = 10, 20, and 40 s) were robust to changes in respiratory patterns after several
minutes. The mimic-predicted target positions after several minutes were computed
based on the previous CM parameters and PIR during the next modeling. The 95th percentiles of the differences between mimic-predicted
and detected target positions over 40 s (E95robust,T: T = 10, 20, and 40 s) were then calculated.
Results
Strong correlations greater than 0.92 were observed between the E95robust,20 and E95robust,40 values. Meanwhile, irregular respiratory patterns with inconsistent amplitudes of
motion created differences between the E95robust,10 and E95robust,40 values of ≥10 mm.
Conclusions
The accuracies of CMs derived using 20 s were almost identical to those obtained over
40 s, and superior to those obtained over 10 s.
Keywords
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Article info
Publication history
Published online: January 29, 2015
Accepted:
January 12,
2015
Received in revised form:
January 10,
2015
Received:
November 7,
2014
Identification
Copyright
© 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.
