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 Pd-103 and I-1 25 radioactive seed sources used in prostate cancer brachytherapy has been measured. Calibration factors relating chamber response (current or dial se tting) to measured air-kerma strength have been determined for seeds from n ine manufacturers, each with different designs. Variations in well-ionizati on chamber response relative to measured air-kerma strength have been obser ved because of differences in the emitted energy spectrum due to bath the r adionuclide support material (I-125 seeds) and the mass ratio of Pd-103 to Pd-102 (Pd-103 seeds). Obtaining accurate results from quality assurance me asurements using well-ionization chambers at a therapy clinic requires know ledge of such differences in chamber response as a function of seed design. [S0094-2405(00)00910-X].