COMPARISON OF THE CALIBRATION FACTOR NGAS FOR A PLANE-PARALLEL IONIZATION-CHAMBER DETERMINED IN CO-60 AND HIGH-ENERGY ELECTRON-BEAMS

Using the protocol of the American Association of Physicists in Medici ne (AAPM) for the determination of absorbed dose from high-energy radi ation, the calibration factor N(gas) for the PTW M23343 plane-parallel ionization chamber has been determined, in Co-60 and high-energy elec tron beams. To do this two cylindrical chambers of different wall mate rials and known values of N(gas) have been used as reference chambers. Our results show that the N(gas) value for the plane-parallel chamber determined in the Co-60 beam is about 2% higher than the value obtain ed in the high-energy electron beams. The discrepancy is attributed to not taking into account a wall correction factor for the plane-parall el chamber while calibrating in the Co-60 beam.