Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level

The purpose of this work was to investigate the feasibility of implementing a megavoltage calibration service for ionization chambers at the secondary standards level. Three reference-class ionization chambers were taken to the National Research Council (NRC) Canada for their primary megavoltage calibration service. Quadratic fits were applied to this data and used to determine calibration coefficients specific to the University of Wisconsin Medical Radiation Research Center (UWMRRC) beam qualities. The primary data and UWMRRC data were used to cross calibrate the three chambers. The resulting calibration coefficients were compared to the NRC values and agreement within 1% was observed. The uncertainty budgets developed for this secondary calibration service were found to be at the same level as those provided for a60Co calibration service at the secondary level. These results indicate that this type of service is feasible at the secondary standards level with the same level of un-certainty as the current standard of practice.