Characterization of the response of a well chamber to different models of Ir-192 sources for HDR brachytherapy

The determination of the reference air kerma rate (KR) with well chambers calibrated using a different model of source than desired can lead to significant errors, affecting both radiological traceability institutions and healthcare facilities. This study employs the methodology proposed by SHIPLEY et al. (2015) with the PTW T33005 well chamber model and six models of HDR brachytherapy sources (microSelectron v.1; microSelectron v.2; Flexisource; GammaMed Plus; BEBIG GI192M11; Varisource VS2000) to derive correction factors for source geometry (KSG). These factors adjust the chamber calibration factor for air kerma (NK) to the source model under measurement. The methodology relies on simulating the chamber response to sources using the Monte Carlo Method (MC), specifically utilizing the MCNPX code. Both the source and well chamber models were validated by comparing dosimetric parameters from TG-43 and simulated calibration factors (MCNK) with literature-derived reference values. The normalized KSG values, relative to the microSelectron v.1 source, agree with reference values, demonstrating the methodology's applicability across various chamber models, sources, and MC codes. The corrections ranged from 0.984 to 1.001, with the most significant correction observed for the Varisource VS2000 source, yielding KSG = 0.984, corresponding to a -1.6% correction.