[en] At present there are no specific primary standards for ¹⁹²Ir high dose rate sources used in brachytherapy. Traceability to primary standards is guaranteed through the method recommended by the AAPM that derives the air kerma calibration factor for the ¹⁹²Ir gamma rays as the average of the air kerma calibration factors for x-rays and ¹³⁷Cs gamma-rays or the Marechal et al. method that uses the energy-weighted air kerma calibration factors for 250 kV x rays and ⁶⁰Co gamma rays as the air kerma calibration factor for the ¹⁹²Ir gamma rays. In order to use these methods, it is necessary to use the same buildup cap for all energies and the appropriate wall correction factor for each chamber. This work describes experimental work used to derive the A_W for four different ionization chambers and different buildup cap materials for the three energies involved in the Marechal et al. method. The A_W for the two most common ionization chambers used in hospitals, the Farmer NE 2571 and PTW N30001 is 0.995 and 0.997, respectively, for 250 kV x rays, 0.982 and 0.985 for ¹⁹²Ir gamma rays, and 0.979 and 0.991 for ⁶⁰Co gamma rays, all for a PMMA build-up cap of 0.550 gm cm-2. A comparison between the experimental values and Monte Carlo calculations shows an agreement better than 0.9%. Availability of the A_W correction factors for all commercial chambers allows users of the in-air calibration jig, provided by the manufacturer, to alternatively use the Marechal et al. method. Calibration laboratories may also used this method for calibration of a well-type ionization chamber with a comparable accuracy to the AAPM method