| LUO Su-ming,HE Zhi-jian,GAO Lei.Development of measurement methodology with reference air kerma of 192Ir source afterloding in bracytherapy[J].Chinese Journal of Radiological Medicine and Protection,2008,28(4):398-400 |
| Development of measurement methodology with reference air kerma of 192Ir source afterloding in bracytherapy |
| Received:October 25, 2007 |
| DOI： |
| KeyWords:Afterloding therapy unit The ion-chamber 192Ir source air kerma |
| FundProject:科技部社会公益研究专项资助(2004DIB1J035) |
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| Abstract:: |
| Objective To develop measurement of reference air kerma for 192Ir sources with NE 2570 electrometer, 2571 ion-chamber and machining measured holder. Methods The measuring holder was placed at the distance of 1m from the walls, the floor and ceiling, the ion-chamber was insert into the polymethyl methacrylate (PMMA) jig of the measuring holder, the optimum distance is 16cm from the source centre to ion-chamber centre. The source was transmitted by the afterloding system to the plastic pipe to measure reference air kerma of the source. According to calibration factors from 60Coγ rays and 250 kV Χ rays with air exposure to calculated the air kerma calibration factor, the air kerma calibration factor of 192Ir source was calculated by 60Coγ rays and the effective energy of the 250 kVΧray beam. The scatter correction factor was given by the shadow shield experiment for the walls, the floor, the air and the measuring holder, the correction factors were given for the attenuation of primary photons in air and the electrons entering the air cavity are mainly generated in the inner wall of the chamber by 1079 report in IAEA. Results Two measuring methods were used for 192Ir source under same environment condition, the ion-chamber and well-type chamber values are 1.584×1011Bq and 1.561×1011Bq respectively, and the relative deviation from them is within 1.4%. Conclusions The air kerma measurement of 192Ir source the ion-chamber with is not depended on the source geometry (point source, line source etc), the size and the material of shell, the shape, the quality of materials and the size of the chamber. The uncertainty error of the air kerma is lessin comparison to the air exposure. |
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