TITLE:
Investigation of Well-Balanced kV X-Ray Imaging Conditions between Skin Dose and Image Noise for Dynamic Tumor Tracking Irradiation
AUTHORS:
Takahiro Nakai, Akira Sawada, Hiroaki Tanabe, Masaki Sueoka, Sho Taniuchi, Kenji Takayama, Takehiro Shiinoki, Yoshitomo Ishihara, Masaki Kokubo
KEYWORDS:
Dynamic Tumor Tracking Irradiation, Skin Dose, Vero4DRT
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.6 No.4,
November
16,
2017
ABSTRACT: 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/QFPDen)0.479, where QFPDen denotes amount of ionization
in front
of FPD. Then, skin dose, D (N, t, v) was formulated as (0.045/N)(1/0.479)/QFPDen/mAs
(t, v) ×D/mAs (v), where QFPDen/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.