AbstractID: 7484 Title: A Secondary Calibration Laboratory Well-Chamber Calibration Proficiency Test
for Ir-192 Ribbon Sources used in Intravascular Brachytherapy
Two secondary calibration laboratories are currently accredited by the American Association of Physicists in Medicine (AAPM) to
perform well-chamber calibrations for Best Ir-192 low-dose-rate (LDR) brachytherapy seeds traceable to the National Institute of
Standards and Technology (NIST). A proficiency test was done to determine whether these secondary laboratories could successfully
calibrate a well chamber for a Cordis ribbon source, used in intravascular brachytherapy, which contains multiple Best Ir-192 seeds in
a single catheter. Two ribbons and a single seed were sent to NIST by Best/Cordis for calibration. The responses of three different
well chambers were measured as a function of vertical position of the ribbon or seed in the well. The air-kerma strength of each
individual seed from a dismantled ribbon was determined by measurement in the NIST spherical aluminum re-entrant chamber,
applying a calibration coefficient derived from primary standard graphite-cavity-ionization chamber measurements. One of the well
chambers, the remaining ribbon, and a single seed were sent to two secondary calibration laboratories, who reported well chamber
calibration coefficients for the seed and ribbon to NIST. The results of this intercomparison, as well as gamma-ray spectrometry
measurements on Ir-192 seeds, will be discussed.