AbstractID: 6569 Title: Calibration of New HDR Ir-192 Sources
The interim standard Air Kerma Strength calibration traceable to NIST for High
Dose Rate (HDR) 192Ir sources has been established at the University of Wisconsin
Accredited Dosimetry Calibration Laboratory (UWADCL) using an in-air 7-distance
technique. This technique uses an ionization chamber that is directly traceable to NIST,
thus providing a calibration with a secondary standard. This measurement has
historically been performed on a Nucletron 192Ir source. However, the emergence of new
sources on the market warrants calibration of the modified sources.
In the present study, refinements are made to the existing 7-distance measuring
apparatus to allow accurate comparison between Nucletron and Varisource 192Ir sources.
The measurements are made with an Exradin A3 spherical ionization chamber with direct
NIST traceability for 137Cs and 250M x-ray energies and an interpolated calibration factor
for 192Ir. The measurements were made with 2 different sources for each afterloader and
at various source strengths. The results are compared with measurements obtained using
the UWADCL standard well chambers calibrated previously, as published in 1991.
These measurements indicate that the calibration factors for both vendors are within the
2% established uncertainty of the 7-distance measurement.