Baylor University Medical Center Proceedings July 2017 - 277

To preserve data uniformity, the gamma analyses and proﬁle analyses were performed using SNC PA software version
6.4.1 from Sun Nuclear Corporation. Dose calculations by
Mobius FX based on the log ﬁles from the VMAT delivery
were exported in a Digital Imaging and Communications in
Medicine (DICOM) format and imported into the SNC PA
software for comparison with ArcCheck measurements and
the Eclipse treatment planning system (TPS) from Varian dose
calculations. Gamma analyses for VMAT plans were conducted
with a dose diﬀerence and distance-to-agreement criterion of
3%-3 mm and 2%-2 mm, respectively. All gamma analyses
used the same algorithm for consistency. Dose proﬁle comparisons were conducted at the same time the gamma analyses were
being conducted in the SNC PA software. The dose proﬁles
were evaluated in the horizontal, vertical, and diagonal directions of the dose plane.

Figure 1. ArcCheck setup for volumetric-modulated arc therapy delivery in a
Truebeam linac.

RESULTS
Proﬁles and gamma analyses were compared on all VMAT
QA plans. The average gamma values with criterion of 3%-3
mm and 2%-2 mm for the comparison for ArcCheck-Mobius
FX, ArcCheck-TPS, and Mobius FX-TPS are presented in
Table 1. Figure 3 presents gamma analysis comparisons of
1) the ArcCheck-measured dose with the Mobius FX dose; 2)
the ArcCheck-measured dose with the Eclipse TPS dose; and
3) the Mobius FX dose calculated based on the linac log ﬁles
with the Eclipse TPS dose calculation. Similar results were
found in the other cases analyzed.
DISCUSSION
In the gamma analyses, comparable values were observed
with the TPS calculation for the 3%-3 mm and 2%-2 mm
criterion among ArcCheck and Mobius FX. When comparing
Mobius FX directly to ArcCheck at the 3%-3 mm criterion,
small discrepancies were observed. When increasing the criterion to 2%-2 mm, larger discrepancies between the methods
were observed. The diﬀerences were observed in diﬀerent regions when comparing Mobius FX and ArcCheck to TPS dose
calculations. As a result of direct comparison between Mobius
FX and ArcCheck, we can check the diﬀerences between both
VMAT QA methods.
Our results showed a similar trend when comparing
Mobius FX to the TPS dose calculations and those acquired
by traditional methods. As the gamma criterion of the analysis
was narrowed, discrepancies between Mobius FX and traditional methods appeared in the analyses due to the diﬀerent

b
Table 1. VMAT QA gamma comparison results among Mobius FX,
ArcCheck measurement, and TPS dose calculation
ArcCheck vs Mobius FX
3%-3 mm
97.74
Figure 2. (a) Mobius FX dose calculation based on linac log files recorded at
delivery of a patient's specific fraction, with a (b) dose volume histogram.
July 2017

2%-2 mm
90.48

ArcCheck vs TPS

Mobius FX vs TPS

3%-3 mm 2%-2 mm 3%-3 mm 2%-2 mm
99.48

96.80

99.96

98.8

VMAT indicates volumetric-modulated arc therapy; QA, quality assurance; TPS, treatment planning system.

Clinical experience with machine log ﬁle software for volumetric-modulated arc therapy techniques

277

Table of Contents for the Digital Edition of Baylor University Medical Center Proceedings July 2017