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
Results
The energy spectrum of diagnostic X-rays and monochromatic X-rays is shown in Figure 3.
The effective energy of each X-ray spectrum is shown in Table 1.
The energy spectra of diagnostic X-rays were broad.
The maximum energy of X-rays corresponds to the tube voltage,
but the minimum energy hardly changes.
Thus,
when the tube voltage changed from 40 to 140 kV,
the effective energy of the diagnostic X-ray varied between 25 and 44 keV.
On the other hand,
the energy spectra of monochromatic X-rays were narrow and the effective energies were around 80% of the value of the tube voltage.
Therefore,
the effective energy of 70 kV diagnostic X-rays and the 40 kV narrow-beam X-rays were the same,
though the shape of the energy spectrum was different.
Figure 4 shows the energy dependence of nanoDot calibration factor.
The response of the nanoDot is at maximum when 20 – 30 keV of photons are irradiated; the response of the nanoDot becomes lower when the energy of irradiated photons becomes higher.
The calibration factor at 140 kV diagnostic X-rays were 25% lower than the calibration factor at 40 kV diagnostic X-rays.
The calibration factors for monochromatic X-rays are the same with the calibration factors for mono-energetic X-rays.
On the other hand,
the calibration factors for diagnostic X-rays were different from the calibration factors for mono-energetic X-rays.
The calibration factor at 70 kV diagnostic X-rays is 5% different from the calibration factor at 40 kV monochromatic X-rays,
which has 32 keV of effective energy.
Furthermore,
the calibration factor at 140 kV diagnostic X-rays is 15% different from 44 keV mono-energetic X-rays.
In the spectrum of 140 kV diagnostic X-rays,
the main component of photons are 59 keV characteristic X-rays emitted by tungsten,
and it is higher than the effective energy of X-rays.
Hence,
the calibration factor at 140 kV diagnostic X-rays is lower than the calibration factor at 44 keV mono-energetic X-rays.