Influence of anode/filtration setup on X-ray multimeter energy response in mammography applications

Abstract

Quality control and assurance of mammography X-ray generators include usage of solid-state detectors and/or ionization chambers which are calibrated in standard reference radiation fields. IEC 61267:2005 standard defines reference mammography radiation fields for Mo/Mo anode/filtration, while various anode/filtration combinations are encountered in clinical mammography X-ray units. Not all Secondary Standard Dosimetry Laboratories have an X-ray generator with Mo/Mo radiation setup, thus traceability can be established only for the available anode/filter combinations which is commonly limited to W/Al. In this study, W/Al radiation fields were established under laboratory conditions by performing half-value layer measurements, and characterization of four solid-state detectors was performed. X-ray multimeter performance was evaluated in terms of energy response in the W/Al radiation fields. In the laboratory conditions the energy response of the dosimeters had larger deviation from unity for dosimeters without appropriate anode/filter combination selected in the software settings, even though most of the dosimeters had uniform relative response. Discrepancy in the response was further investigated by examining its variation induced by available detector software settings, and it was determined that the dosimeter response can vary up to 20 %. In clinical setup, half-value layer was determined, and detector performance was examined. Dosimeters were tested in clinical fields with Mo/Mo, Mo/Rh, W/Rh, W/Ag anode/filter combinations in the X-ray tube voltage range from 25 kV to 35 kV. For most clinical radiation fields, multi-element detectors had energy response deviation within ±5 %. The single-element detector had one software setting available and has exhibited strong energy dependence. Extensive testing of detector response such as presented in this paper allows for correction factor interpolation based on half-value layer.