Measurment of activity of 125I seed source

For controlling the quality of the radiotherapy in which seed sources are implanted in the tissue to treat the cancer and avoiding the medical accident of exposure. 10% (5 seeds) of 50 seeds are checked and it is required that the relative deviation of apparent activity of seed sources between measured value and vendor's is within the range of 5%. The paper introduces the calibration method of 125I sources used in clinic of our hospital. The Air Kenna Rate of 125I sources is determined by the well-type ionization chamber. Thereafter the apparent activity of 125I sources is calculated and measured results are analyzed. The results show that 80% of 125I sources are up to grade. (authors)