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New X-CT Dose Calibration Method Using Polymer Gel Dosimeter

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J Ota

j ota*, R Kurosawa , T Kobayashi , M Yoshitada , K Chida , Chiba Univercity Hospital, Chiba City, Chiba,Japan


SU-I-GPD-J-39 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Monte Carlo simulation is one of the possible ways of evaluating the dose distribution inside the body. But it requires additional validation between the calculated dose distribution and the actual one. We measured the dose provided by CT using a polymer gel dosimeter which potentially can measure the 3D dose distribution. It is, however, difficult for the polymer gel dosimeter to measure the low-dose such as 500 mGy or less due to the ambiguity of the Dose-R2 calibration curve in that region.

Methods: CT used Aduilion ONE (Toshiba medical systems, Japan).Comparing the conventional method and newly devised method.In the conventional method, calibration vials were irradiated to different well-defined doses to create a Dose - R2 calibration curve. In the proposed method, one 720ml-phantom was irradiated with three well-defined doses over three different areas.

Results: To read the dose value, we used the R2 value of MRI.In the conventional method, Gel 1 was y = 0.0057 x, R²= 0.6517, gel 2 was y = 0.002 x, R² = 0.7822. The coefficient of variation of the slope of the two curves was 0.679.The newly devised method, Gel 1 was y = 0.0008 x, R² = 0.9895, gel 2 was y = 0.0008 x, R² = 0.9323. The coefficient of variation of the slope of the two curves was 0.

Conclusion: By using the newly devised method we were able to measure doses down to 80 mGy.If dosimetry of a CT apparatus using a gel dosimeter can be carried out accurately, it is possible to efficiently verify tube current / tube voltage modulation, simulation verification, etc.

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