Well‐ionization chamber response relative to NIST air‐kerma strength standard for prostate brachytherapy seeds

The response of well-ionization chambers to the emissions of 103 Pd and 125 I radioactive seed sources used in prostate cancerbrachytherapy has been measured.Calibration factors relating chamber response (current or dial setting) to measured air-kerma strength have been determined for seeds from nine manufacturers, each with different designs. Variations in well-ionization chamber response relative to measured air-kerma strength have been observed because of differences in the emitted energy spectrum due to both the radionuclide support material ( 125 I seeds) and the mass ratio of 103 Pd to 102 Pd ( 103 Pd seeds). Obtaining accurate results from quality assurancemeasurements using well-ionization chambers at a therapy clinic requires knowledge of such differences in chamber response as a function of seed design.