COMPARISON OF NIST AND MANUFACTURER CALIBRATIONS OF SR-90-90 OPHTHALMIC APPLICATORS(Y)

Since the resumption of the NIST calibration service for Sr-90+Y-90 be ta-particle ophthalmic appli cators, 65 sources have been calibrated u sing the revised technique [C. G. Soares, Med. Phys. 18, 787-793 (1991 )]. For 59 of these sources, the manufacturer's calibration results we re available for comparison to the NIST calibration results. The 59 so urces represent eight different manufacturers, only one of which is st ill selling new sources. Manufacturer Calibration dates range from the present back to 1954. The results of the comparisons are presented, b roken down by both manufacturer and calibration date; there are intere sting and significant trends in both, with average differences of 20% not uncommon. The obsolete unit, ''roentgen-equivalent-beta'' (reb), i n which some of the manufacturer calibrations are expressed, is discus sed, and a factor (0.00982 Gy reb(-1)) for its conversion to absorbed dose is suggested.