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Keywords:
Radioprotection / Radiation dose, Management, Experimental, Dosimetry, Dosimetric comparison
Authors:
K. Takegami1, H. Hayashi1, K. Nakagawa1, H. Okino1, T. Okazaki 2, I. Kobayashi2; 1Tokushima/JP, 2Tsukuba, Ibaraki/JP
DOI:
10.1594/ecr2015/C-0218
Results
Figure 7 shows two calibration curves obtained by two experimental conditions of free air (Setup A of the left figure) and using the phantom (Setup B of the right figure).
The horizontal and vertical axes in each figure show air-kerma or ESD and counts/e,
respectively.
Here,
e represents an intrinsic detection efficiency.
These axes represent the logarithmic expression.
In the left figure,
the counts are proportional to the air-kerma as shown in the red straight line.
In the right figure,
the relationship between the counts and ESD derived via correction of the BSF shows good linearity.
As a result of comparison between the two calibration curves,
we found that the calibration curve of free air condition is in good agreement with that of the phantom.
It means that we can derive the air-kerma and/or ESD using this unique calibration curve.
For the evaluation of the calibration curve,
we investigated a deviation of experimental data from the calibration curve.
Figure 8 shows the deviation.
The horizontal axis shows a ratio of the measured to derived values.
Open and close circles show the data of free air (experiment of Setup A) and using the phantom (experiment of Setup B),
respectively.
As shown in Fig.8,
all data are included within a 10% area.
It means that our measurement method can derive the air-kerma or ESD with an accuracy of 10%.
Finally,
we exemplify preliminary experiments toward the clinical application of the nanoDot dosimeter.
Figure 9 demonstrates experimental setups and measurement results of ESD in the chest X-ray diagnosis.
The nanoDot dosimeter and the thermo luminescence dosimeter (TLD) were put on the chest phantom as shown in upper photographs of Fig.9.
The ionization chamber was arranged in free air.
Dosimeters were irradiated at the following conditions: the tube voltage is 120 kVp,
the tube current-time product is 5.6 mAs and the source to dosimeter distance is 172 cm,
which is the general condition in Japan [15].
Here,
ESD measured by the nanoDot dosimeter was derived using the calibration curve obtained in our study.
ESDs which are derived by the nanoDot dosimeter,
the TLD and the ionization chamber were 0.24±0.014,
0.272±0.04 and 0.261±0.013 mGy,
respectively.
A guidance level of IAEA [16] which is an upper recommendation value of the exposed dose for the chest radiography and measured values reported by Matsunaga et al.
[15] and Asada et al.
[17] were indicated as comparison data shown in the graph of Fig.9.
These values were 0.4,
0.24 and 0.27 mGy,
respectively.
They are consistent with each other.
In the represented methods,
only our method can be applied in a clinical situation.
Using the nanoDot dosimeter,
direct measurement of ESD for each patients is hoped for.