The Well-type ionization chamber (WIC) is the standard method to measure the Air- Kerma strength K_a,100for the Ir-192 source, the aim of this study is to validate the K_a,100 using PTW Al T9193 phantom. 

For phantom measurement, Farmer chamber PTW 30012-1, with volume of 0.6 cc and electrometer PTW UNIDOS E were used. The chamber has a calibration factor in terms of N_D,wat a reference beam quality Co-60.

The phantom is 20-cm diameter with 4 holes at the edges for detector adaptors and one hole at the center for afterloading applicator. For the WIC measurements, Standard Imaging HDR-1000 plus with its electrometer used in this work.

the following formula was applied to calculate the K_a,100
 

Ka,100 = M_PMMA x N_D,w x K_Q x (1-g_w)^-1 x t_a,w x K_{wp x} K'_zp x K_v x K_r 

Where MPMMA is the collected charge per time interval (nC/min), K_Q correction factor for beam quality, (1-g_w)^-1 correction factor for energy loss due to bremsstrahlung, t_a,w is the mass energy absorption coefficients of air to water, Kwp correction factor for perturbation of radiation field between water and PMMA, K'_zp correction factor for the influence of the PTW phantom, K_v correction factor for volume effect of the ionization chamber. K_r correction factor to account for the different distances between measurement (8cm) and reference point (100cm). All factors were calculated using Monte Carlo simulation EGSnrc code (Ubrich F. 2013). The K_a,100 was measured for five Ir-192 sources. 

The ratio of K_A,100,PMMA/K_{A,100,HDR-1000} is approximately constant from one source to another with a mean value equal to 0.997±0.005 (-0.28%). 

The results underline the equivalence of in-phantom calibration method to the WIC. The K_a,100 are estimated from readings of the ionization chamber calibrated in terms of N_{D, W}. The mean deviations were 0.63% ± 0.1. However, a high degree of agreement was demonstrated over the five sources.