UNIFORMITY AND DOSE PROFILES OF IEC 61267 RQT-8, RQT-9 AND RQT-10 RADIATION QUALITIES

Dosimetry in diagnostic radiology requires the use of specialized instrumentation, the design and performance of which must be matched to the needs of the clinical situation. These instruments have to be calibrated to be traceable to national or international standards. The IAEA ensures traceability of radiation measurements through the IAEA/WHO network of Secondary Standards Dosimetry Laboratories (SSDLs) and Secondary Standard Dosimetry Laboratory at Ruđer Bošković Institute (RBI/SSDL) is a member of the network. Calibrations are performed in compliance with TRS457 [1] which is the code of practise for calibrations in diagnostic radiology. Calibrations are performed in the X ray field in different beam qualities. The qualities at RBI/SSDL are established according to IEC 61267 [2]. Calibrations should be performed in radiation fields with air kerma rate within the sensitive volume of the detector not to vary more than 5% according to standard 4037-1 [4]. Uniformity of radiation field is influenced by spectral distribution of x-rays, finit focus dimensions, Heel effect and aging of anode. Our aim was to investigate uniformity and dose profiles of IEC 61267[2] RQT-8, RQT-9 and RQT-10 radiation qualities. These qualities simulate the unattenuated beam used in CT diagnostic radiology. Establishment of these qualities requires establishment of radiation qualities RQR IEC 61267[2] which are used for measurements in the radiation beam as emerging from the x-ray source assembly. Such radiation qualities are, for example, applied for determining characteristics of patient supports in case the patient support is situated in between the x-ray source assembly and the patient. When these qualities are established, copper filtration is added to generate RQT qualities.