Author(s)

Takahiro Nakai¹, Akira Sawada^2*, Hiroaki Tanabe³, Masaki Sueoka³, Sho Taniuchi³, Kenji Takayama⁴, Takehiro Shiinoki⁵, Yoshitomo Ishihara⁴, Masaki Kokubo^6,7

¹Department of Radiological Technology, Kobe City Medical Center General Hospital, Kobe, Japan.
²Faculty of Medical Science, Kyoto College of Medical Science, Nantan, Japan.
³Department of Radiological Technology, Institute of Biomedical Research and Innovation, Kobe, Japan.
⁴Department of Radiation Oncology and Image-Applied Therapy, Kyoto University, Kyoto, Japan.
⁵Department of Radiation Oncology, Yamaguchi University, Ube, Japan.
⁶Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Kobe, Japan.
⁷Department of Radiation Oncology, Kobe City Medical Center General Hospital, Kobe, Japan.

Purpose: The purposes of this study were to estimate accumulated kV X-ray imaging dose throughout dynamic tumor tracking (DTT) irradiation by Vero 4DRT system and to address an analytical skin dose formula for well-balanced kV X-ray imaging conditions between skin dose and image noise. Method: First, skin dose was measured using kV X-ray tube, chamber, and water-equivalent phantoms. Next, imaging dose for six patients in DTT treatment was computed using log files. Subsequently, scattered dose ratio was calculated by amount of ionization in front of flat panel detector (FPD) for fields with size of maximum and the chamber for 0 - 200 mm-thickness phantoms and tube voltage of 60, 80, 100, 120 kV, respectively. Furthermore, image noise was computed from FPD images. Results: The skin dose was greater by a factor of 1.4 - 1.6 than those in Synergy XVI system. The image noise in FPD,  was expressed as N = 0.045×(1/Q_FPDen)^0.479, where Q_FPDen denotes amount of ionization in front of FPD. Then, skin dose, D (N, t, v) was formulated as (0.045/N)^(1/0.479)/Q_FPDen/mAs (t, v) ×D_/mAs (v), where Q_FPDen/mAs (t, v) and D_/mAs (v) denote amount of ionization in front of FPD and skin dose per mAs, respectively. Using the formulae, it has been demonstrated that skin dose with 120 kV has become lower than any other tube voltage in this study. Conclusion: Using skin doses for the phantom, the skin dose throughout DTT irradiation was estimated as 0.50 Gy. Furthermore, skin dose by kV X-ray imaging was described as a function of image noise, phantom thickness, and tube voltage, suggesting image noise may be reduced with higher X-ray tube voltage in this phantom study.

Dynamic Tumor Tracking Irradiation, Skin Dose, Vero4DRT

Nakai, T. , Sawada, A. , Tanabe, H. , Sueoka, M. , Taniuchi, S. , Takayama, K. , Shiinoki, T. , Ishihara, Y. and Kokubo, M. (2017) Investigation of Well-Balanced kV X-Ray Imaging Conditions between Skin Dose and Image Noise for Dynamic Tumor Tracking Irradiation. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 6, 410-420. doi: 10.4236/ijmpcero.2017.64037.