A chamber and electrometer calibration factor as determined by each of the five AAPM accredited dosimetry calibration laboratories.

The same calibration grade ionization chamber and electrometer were sequentially sent to all five currently AAPM Accredited Dosimetry Calibration Laboratories (ADCL). A Cesium-137 based check device was utilized to ensure chamber and electrometer factor constancy and showed a maximum deviation of 0.32% (typically less than 0.1%) over the 227 days needed to complete the intercomparison. The chamber and electrometer calibration factor provided by each of the five ADCLs were analyzed for consistency. The maximum percent difference in reported chamber factor between all five ADCLs was 1.40%. The reported electrometer factor had a maximum discrepancy of only 0.50%. System (chamber plus electrometer) factors as provided by three of the five ADCLs had a maximum discrepancy of 1.51%.