Establishment of the practical peak voltage for standard computed tomography radiation qualities at a Calibration Laboratory

At the Calibration Laboratory of IPEN/CNEN-SP (LCI) several radiation qualities were established, and they are in use for the calibration of radiation detectors for clinical and industrial uses. In order to follow international recommendations, a new quantity has been established at the LCI, the practical peak voltage (PPV). In this work, an analysis of this quantity was made for the computed tomography standard radiation qualities RQT8 and RQT9. The PPV and the mean and peak kilovoltage values were measured with a noninvasive Radcal Accu-kV Diagnostic Sensor, model 40X12-W meter. In order to compare the results obtained for PPV a Physikalisch-Technische Werkstätten (PTW) meter, model Diavolt, was also utilized. The tests were performed with an X-ray system Pantak/Seifert, tube model MXR-160/22 (constant potential). The measurements were taken varying the distance between the focal spot and the meters. The uncertainties attributed to the quantities of kV and PPV for a noninvasive method did not exceed 5%, and therefore they were within the IAEA recommendations. In the corresponding measurements, increasing the distance between the focal spot and the meter, the PPV and the kV values should be constant. The results were within the predictions, and the PPV and the kV values presented variations within international recommendations. This type of quality control procedure is very important to verify the good reliability of the X-ray system of LCI, because it is utilized for routine calibration of dosimeters.