Purpose: Respiratory-gated radiation therapy (RT) using the real-time
tumor-tracking radiotherapy (RTRT) system is an effective technique for
managing tumor motion. High dosimetric and geometric accuracy is needed;
however, quality assurance (QA) for respiratory-gated RT using the RTRT system has not been reported. The purpose of
this study was to perform QA for respiratorygated RT using the RTRT
system. Materials and Methods: The RTRT system detected the position of the fiducial
marker and radiation delivery gated to the motion of the marker was performed.
The dynamic anthropomorphic thorax phantom was positioned at the isocenter
using the fiducial marker in the phantom. The phantom was irradiated only when
the fiducial marker was within a three-dimensional gating window of ±2 mm from
the planned position. First, the absolute doses were measured using anionization
chamber inserted in the phantom under the stationary, gating and non-gating
state for sinusoidal (nadir-to-peak amplitude [A]: 20 - 40 mm, breathing period
[T]: 2 - 4 s) and the basic respiratory patterns. Second, the dose profiles
were measured using Gafchromic films in the phantom under the same conditions. Differences
between dose profiles were calculated to evaluate the dosimetric and geometric
accuracy. Finally, differences between the actual and measured position of the
fiducial marker were calculated to evaluate the tracking accuracy for
sinusoidal and basic respiratory patterns. Results: For the sinusoidal patterns,
the relative doses were 0.93 for non-gating and 0.99 for gating (A = 20 mm, T =
2 s), 0.94 for non-gating and 1.00 for gating (A = 20 mm, T = 4 s), 0.55 for
non-gating and 1.00 for gating (A = 40 mm, T = 4 s), respectively. For the basic
respiratory pattern, the relative doses were 1.00 for non-gating and 1.00 for
gating, respectively. Compared to the stationary conditions, the differences in
lateral distance between the 90% dose of dose profiles were 6.23 mm for
non-gating and 0.36 mm for gating (A = 20 mm, T = 2 s), 8.79 mm for non-gating
and 1.73 mm for gating (A = 20 mm, T = 4 s), 18.37 mm for non-gating and 0.67
mm for gating (A = 40 mm, T = 4 s), respectively. For the basic respiratory
pattern, those were 5.23 mm for non-gating and 0.35 mm for gating. The root
mean square (RMS) values of the tracking error were 0.18 mm (A = 20 mm, T = 2
s), 0.14 mm (A = 20 mm, T = 4 s), and 0.21 mm (A = 40 mm, T = 4 s) for
sinusoidal and 0.79 mm for the basic respiratory pattern, respectively. Conclusion:
We conducted QA for respiratory-gated RT using the RTRT system. The respiratory-gated
RT using the RTRT system reduced the blurring effects on dose distribution with
high dosimetric and geometric accuracy.