A parallel plate chamber for calibration of 192Ir LDR and HDR sources.

A good program of quality assurance requires the user to check the calibration of brachytherapy sources. Conventional well-type ionization chambers have restrictions on the length of the source which can be used due to the variation in the relative ionization with distance from the position of maximum sensitivity. We have fabricated a parallel plate chamber, which can be used for both LDR and HDR sources of 192Ir placed centrally inside. The electrodes are made from printed circuit boards. Sources of lengths up to 15 cm can be calibrated with this chamber. It has a good linear response and stability. It costs little and can be used with any electrometer. The chamber, which has a volume of about 40 cm3, has a response of 820 nCmin(-1) per cGy m2 h(-1).