Author(s)

Hideaki Hirashima¹, Mitsuhiro Nakamura^1,2*, Yoshitomo Ishihara¹, Nobutaka Mukumoto¹, Mami Akimoto¹, Tsuneyuki Tomita³, Yoshinori Hirose³, Kenji Kitsuda³, Takashi Ishigaki⁴, Takashi Mizowaki¹

¹Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
²Department of Information Technology and Medical Engineering, Faculty of Human Health Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
³Division of Radiology, Osaka Red Cross Hospital, Osaka, Japan.
⁴Department of Radiation Therapy, Osaka Red Cross Hospital, Osaka, Japan.

Introduction: To compare the measured dose distributions to calculated ones in dose-to-water (D_w) and dose-to-medium (D_m) 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 D_w and D_m. The change in γ3%G/3mm between D_w and D_m were statistically analyzed using JMPPro11 software. Results: The median values of γ3%G/3mm for all simple plans for D_w and D_m 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 D_w and D_m 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 D_w, but were not for D_m. From the viewpoint of the rationale of dosimetry, D_w shows better agreement with measured dose distribution when using the fixedphantom density recommended by the vendor.

Helical Diode Array Dosimeter, Dose-to-Water, Dose-to-Medium, Gamma Pass Rate

Hirashima, H. , Nakamura, M. , Ishihara, Y. , Mukumoto, N. , Akimoto, M. , Tomita, T. , Hirose, Y. , Kitsuda, K. , Ishigaki, T. and Mizowaki, T. (2018) 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. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 7, 74-86. doi: 10.4236/ijmpcero.2018.71007.