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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
Aims and objectives
X-ray diagnoses for detection of lesion locations,
such as,
various cancer and inflammatory disorders are in widespread use at hospitals around the world.
Up to now,
dose exposure has increased because a sufficient dose is need for a high quality image which supports an accurate X-ray diagnosis.
As a result,
many researches investigate the improvement of image quality.
On the other hand,
little is reported on a dose measurement for management of the personal exposed dose.
For a proper management of medical irradiations,
entrance skin dose (ESD) should be measured.
In this paper,
we release a report concerning the measurement of personal exposed dose using our new method toward a clinical application.
Generally,
ESD is assumed using an ionization chamber based on an air-kerma measurement with the consideration of a back scatter factor [1-3] (BSF) as shown in Fig.1a).
In the real situation of the X-ray diagnosis,
it is impossible to measure the ESD using the general method because the radiation detector has an effect on the medical image.
Using our new method,
it is expected to measure ESD directly including the contribution of back scattered X-ray in Fig.1b).
Recently,
a small-type optically stimulated luminescence (OSL) dosimeter named “nanoDot” (Fig.2a)) and a reading device of the dosimeter named “microStar” (Fig.2b)) were commercialized by Landauer,
Inc.
The nanoDot dosimeter is mainly used to manage the exposed dose of the patient in the radiotherapy region [4-6],
whereas only a small number of papers were reported for the dosimetry of diagnostic X-ray [7-9].
For a use of the dosimeter in the diagnosis X-ray region,
the following three characteristics become advantageous compared to other detectors [10,
11]: first,
being similar in density with that of a human body,
second,
having a low detection efficiency,
and third,
formation of a small size detection area(10×10×2 mm,
Fig.2a)).
As a result of these characteristics,
the dosimeter does not affect the medical image as represented in elbow radiograph (Fig.3).
The nanoDot dosimeter is expected to be a useful dosimeter for the management of personal exposed dose in clinical settings [12].
In order to measure ESD using the nanoDot dosimeter,
the measurement value needs to be calibrated to ESD estimated by an ionization chamber.
In this study,
a calibration curve which is a relationship between the measured value of the nanoDot and ESD estimated by the general method (ionization chamber) was derived experimentally.
The calibration curves were derived in two conditions,
free air and using a phantom.
They were compared to each other.