Construction and calibration of a multipurpose instrument to simultaneously measure dose,voltage and half-value layer in X-ray emission equipment

This work reports on the development of a multipurpose instrument that simultaneously measures delivered dose (air kerma), peak voltage (kVp) and half value layer (HVL) in X-ray machines. The device will help control quality of X-ray equipment routinely used in diagnostic and interventional radiological procedures. The measuring device is equipped with several attenuating filters of different materials and thicknesses, and Gafchromic^® XR-QA2 radiochromic films are used as sensitive elements. The films are scanned after being irradiated and the resulting color intensities indicate a relationship between the degree of film darkening under each individual filter and the quantities of interest, i.e. air kerma, kVp and HVL. Comparing HVL values measured using the proposed multipurpose instrument with those of a reference standard ionization chamber, discrepancy reached 8.4%. As for the kVp evaluation, anomalous results were observed for low atomic number materials and small thicknesses, especially for peak voltages higher than 70 kVp. However, for materials with higher Z and reasonable thickness, the calibration curve R × kVp was quite satisfactory, being R the ratio between the color intensities obtained with two distinct filters. We have also observed a decrease in the influence of Tungsten characteristic radiation on the calibration curve. These results suggest that the proposed instrument may be satisfactorily used to routinely control quality of X-ray equipment, estimating the radiation dose resulting from the direct beam, the applied voltage across the electrodes and the half value layer.