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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
Methods and materials
In our experiments,
X-ray irradiations were carried out using the diagnostic X-ray equipment (Toshiba medical systems corporation,
MRAD-A 50S/70).
The nanoDot OSL dosimeter and the microStar (Landauer incorporation) were also used as shown in Fig.2.
Figure 4a) shows a schematic drawing of the counting system in the microStar system.
The measured value “count” is obtained by counting the blue light photon.
Figure 4b-1) and -2) represent energy levels [4,
13] of the nanoDot dosimeter.
In Fig.4b-1),
when X-ray is irradiated the nanoDot dosimeter,
electrons are excited to the conductor band. At that time,
most of electrons are promptly de-excited to the luminescent center following a blue light emission.
Others will be trapped in the high energy state of an impure substance (Carbon).
These trapped electrons retain information of the X-ray irradiation.
When retaining information is read out,
the green light is irradiated to the trapped electrons as shown in Fig.4b-2).
Here,
they move to the exited level again,
and are de-excited promptly with the emission of blue light.
In this way,
the measurement value “count” of the nanoDot dosimeter is derived.
For the precise experiment,
the nanoDot dosimeter was annealed using our annealing device as shown in Fig.5 [14].
The annealing device consists of four fluorescent light tubes emitting blue light.
We can use sufficiently annealed dosimeters for the following experiment and an efficient cycle of irradiation-reading out-annealing is performed.
Figure 6 shows the experimental method in order to obtain two calibration curves.
First,
in the free air condition (Setup A in Fig.6),
the air-kerma was measured using an ionization chamber (PTW,
DC300).
X-ray was irradiated at the following conditions: a tube voltage is 83 kVp,
a source to dosimeter distance is 200 cm and tube current-time products are 100,
160,
200,
250 mAs.
In the same manner of the free air condition,
the count was measured using the nanoDot dosimeter (Setup A in Fig.6).
To compare these different measured values,
a calibration curve in the free air condition was made.
Second,
using a water-equivalent phantom (Kyoto kagaku corporation limited),
the nanoDot dosimeter put on the phantom was irradiated (Setup B in Fig.6).
Four phantoms (300 mm wide,
300 mm high and 50 mm thick×4) were used.
X-ray was irradiated using three conditions (irradiation fields: 10×10,
20×20,
30×30 cm2 at the surface of the phantom) and the corresponding counts were obtained.
ESD of these condition were estimated by correction of the BSF based on the measured values by the ionization chamber.
Using these measured values,
a calibration curve was derived.
Finally,
two calibration curves obtained in experiments for the free air condition (Setup A) and the phantom (Setup B) were compared.