Keywords:
Quality assurance, Kv imaging, Radiation safety, Physics, Laboratory tests, Experimental, Radioprotection / Radiation dose, Radiation physics
Authors:
T. Okazaki 1, H. Hayashi2, S. Goto3, T. Asahara4, E. Tomita2, Y. Kanazawa4, T. Hashizume1, V. Cruz1, W. H. Cheng1; 1Tsukuba/JP, 2Kanazawa/JP, 3Kanazawa, Ishikawa/JP, 4Tokushima/JP
DOI:
10.26044/ecr2019/C-0212
Aims and objectives
Exposure to diagnostic X-rays provides certain benefits for patients.
At the same time,
it involves some risks such as the development of cancer [1].
To assess the level of risk of radiation exposure in X-ray diagnosis,
evaluation of the irradiated dose is essential.
One useful method to evaluate the dose precisely is to measure the irradiated dose directly by wearing a dosimeter during diagnosis.
Thus,
we have studied the applicability of the nanoDot,
a small type optically stimulated luminescence (OSL) dosimeter,
for dosimetry in the field of X-ray diagnosis [2-6].
The 10×10×2 mm3 of nanoDot dosimeter does not disturb medical diagnosis.
Also it is invisible in an X-ray image since it is composed of Al2O3:C and plastic resin.
The dose irradiated to the nanoDot can be evaluated by the microStar,
a portable OSL reader,
shown in Figure 1. The microStar reader uses green LED lights to stimulate the nanoDot which will results in the emission of blue light by the OSL element.
The amount of luminescence,
or “photon counts”,
emitted by the OSL element is measured by a photomultiplier tube inside the microStar; the amount of luminescence is proportional with the irradiated dose.
The measured photon counts are corrected with respect to the sensitivity of each individual nanoDot,
and the calibration factor of the reader.
This is a simple process in evaluating the radiation dose [7,8].
Since the response of nanoDot has energy dependence and it tends to vary in the energy range of diagnostic X-rays [9,10],
proper dose calibration is necessary for an accurate dose evaluation at each diagnostic X-rays energy range.
Asahara et al.
argue that the calibration factor can be determined by the function of the energy spectrum of incident X-rays and response of the nanoDot at each energy spectrum [8].
Still,
it is difficult to estimate the spectrum of incident X-rays to a nanoDot with complexed irradiation conditions.
Thus,
there are reports evaluating the energy dependence of the nanoDot based upon the effective energy of incident X-rays [10,11].
On the other hand,
some studies reported that the energy dependence of the nanoDot varies depending on the spectrum of incident X-rays,
although the effective energy is the same [5,6,10].
In addition,
there are previous studies that evaluated the nanoDots response to mono-energetic photons [3,9].
In this paper,
we evaluated the influence of the X-ray spectrum on the nanoDot calibration factor in the diagnostic X-rays energy range by Monte Carlo Simulation.