The dependence ofNKRversus KR: the initial, thermal, volumetric recombination and screening effect on the efficiency of collected charges on the calibration of si HDR1000 plus well chambers with192Ir HDR sources.

By using the statistical techniques of the ANOVA means test and regression, it was found that theNKRcalibration factor of Standard Imaging (SI) model HDR 1000 plus chambers presents a quadratic dependence with the Reference air kerma rateKR(from 6.9 mGy h-1to 43.9 mGy h-1). In order to understand and correct this dependency one model is presented for total recombination:ks=I300I150=1+kini+kd+kvol·I300+kscreen·I3002,wherekiniis the initial recombination,kvolthe thermal diffusion recombination,kvolthe volumetric recombination andkscreenthe screening for the currents/charges collected at the potential differences of 300 and 150 V. In conclusion, the total recombinationksis composed by onekiniwith a constant contribution of 0.019%, onekdcontribution of 0.017%, onekvol·I300contribution from 0.022% to 0.138%, and thekscreen·I3002effects from 0.002% to 0.09% in the range ofK̇Rrate above. However, when this model forksis applied to try to correct the quadratic dependence of theNKRversusKR,explicitly there is no improvement in the variation range of 0.5% of theNKRversusKR.Nonetheless, it allows to obtainNKRvalues consistent with auc ≤ 0.7%, which is less than 1.25% reported in the literature by ADCLs or SSDLs.