Effect of varying HVL values on dose output of plain X-ray machines at a fixed kV of 80.

Abstract

Background HVL in diagnostic X-ray machine is an important property that is used to define the penetrating ability of an X-ray beam and hence can be used to determine the component of beam hardness. Purpose The purpose of the study was to assess the effect of HVL on the dose output of diagnostic X-ray machine and to determine the different corrective actions for the cases which did not comply the established dose limits. Material and Methods The study utilized the findings of the radiation safety inspections conducted between 2021–2022 by Atomic Energy Council to investigate different Half value layer (HVL) ranges for diagnostic X-ray machines. A number of 64 X-ray machines were selected for the study based on a set criterion. Results A total of 26 X-ray machines failed the HVL test though produced different descriptions of measured dose output. Fifteen (15) X-ray machines produced doses within the permissible range of 0.025 mGy/mAs – 0.080 mGy/mAs, eight (08) X-ray machines produced doses below the lower limit of the dose range of 0.025 mGy/mAs, while three (03) X-ray machines produce doses above the upper limit of the dose range of 0.080 mGy/mAs. The other 38 X-ray machines passed the HVL test but failed the dose output test. These were classified in different HVL groups that exceeded the recommended regulatory limit, that is, moderate (5), high (19), very high (10) and extreme high (4) X-ray machines. The corrective action made was either adding or removing filter plates to enhance or minimize the filtration for machines that failed the HVL test and the ones that passed HVL test but failed the dose output test respectively. However, this should only be after a conclusive investigation of checking the accuracy of tube current (mA), timer (s) and tube potential (kVp) parameters. Conclusion Therefore, the corrective action for HVL should not be done in isolation from other machine dose contributing parameters like tube current potential parameters and exposure time. The regulatory body recommends that HVL tests should be part of the acceptance and commissioning tests for the new machines and done routinely for the machines in use as specified in the quality control program for each facility.