TITLE:
Comparison of Gamma Pass Rate between the Dose-to-Water and Dose-to-Medium Reporting Modes for Patient-Specific QA Using a Helical Diode Array Dosimeter with a Fixed Phantom Density
AUTHORS:
Hideaki Hirashima, Mitsuhiro Nakamura, Yoshitomo Ishihara, Nobutaka Mukumoto, Mami Akimoto, Tsuneyuki Tomita, Yoshinori Hirose, Kenji Kitsuda, Takashi Ishigaki, Takashi Mizowaki
KEYWORDS:
Helical Diode Array Dosimeter, Dose-to-Water, Dose-to-Medium, Gamma Pass Rate
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.1,
February
23,
2018
ABSTRACT: Introduction: To
compare the measured dose distributions to calculated ones in dose-to-water (Dw) and
dose-to-medium (Dm)
reporting modes for simple plans and patient-specific intensity modulated radiation
therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans using ArcCHECK
with a fixed phantom density. Methods: The recommended density value of
1.18 g/cm3 for Acuros XB and X-ray voxel Monte Carlo was assigned to
ArcCHECK on CT images. A total of 45 simple plans, including a 1-field plan, a
3-field plan, a 4-field plan, a half-arc plan from 270° to 90°, and a full-arc plan, were assessed.
Subsequently, the patient-specific 96 IMRT and VMAT plans were evaluated. Gamma
analysis with a 3% normalized global dose error and a 3 mm distance-to-agreement
criteria (γ3%G/3mm) was performed in the Dw and Dm. The
change in γ3%G/3mm
between Dw and Dm were
statistically analyzed using JMPPro11 software. Results: The median
values of γ3%G/3mm
for all simple plans for Dw and Dm were
98.1% (range, 75.2% - 100%)
and 95.5% (range, 23.7% - 100%),
respectively (p 0.01). In the patient-specific IMRT and VMAT plans,
the median values of γ3%G/3mm for Dw and Dm were
98.6% (range, 90.1% - 100%)
and 90.5% (range, 38.5% - 97.2%),
respectively (p 0.01). Conclusion: Our results showed that
the calculated and measured dose distributions were in good agreement for Dw, but
were not for Dm. From
the viewpoint of the rationale of dosimetry, Dw shows
better agreement with measured dose distribution when using the fixedphantom
density recommended by the vendor.