Development and performance testing of a chamber for absorbed dose in water absolute measurement for 125I brachytherapy seeds

The application of more and more low-energy, low-dose-rate photon radiation seeds in brachytherapy. According to the TG43 report and TG43-U1 report issued by the American Association of Physicists in Medicine, both apparent activity and air kerma strength are physical characterization parameters of brachytherapy seed strength,which are needed to convert into water absorbed dose at the depth of 1 cm. At present, the method of obtaining the water absorbed dose is to convert the air kerma strength, the uncertainty of results exceeds 5% (k = 1), which could reduce the cure rate of the treatment. In order to address this issue ,the China Institute of Atomic Energy has designed a device that can directly replicate the water absorbed dose of 125I brachytherapy seeds,which is an extrapolation chamber embedded with water equivalent material. In order to evaluate the performance of the extrapolation chamber, a series of experiments were carried out, including partial pressure test, leakage current, saturation curve, response linearity, collection area and zero point position. The test results show that the performance parameters of the extrapolation chamber meet the relevant requirements.