Improving the approach to calculating shielding in computed tomography rooms

Abstract

The study assessed the acceptability of the currently existing approach to calculating shielding in computed tomography rooms and formulated proposals for its improvement, taking into account the parameters of research in domestic medical practice. It is proposed to use the dose-length product as the main measured parameter in the new approach to calculating shielding. Typical tomograph workload values of dose-length product, typical for examinations in the Russian Federation, were assessed. Using thermoluminescent detectors, the experimental assessment of the distribution of absorbed dose in the air in a computed tomography room was carried out. The experimental results showed that the distribution of of X-ray exposure in the central plane is not isotropic. Due to the attenuation of exposure by the gantry design, “shadow” zones are observed, where the absorbed dose reduction in the air reaches 10-13 times compared to its level in the direction of couch movement. Based on the results of measurements of the distribution of absorbed dose in air, the relative scatter coefficients were calculated. The workload was determined for 7 tomographs (1 in St. Petersburg and 6 in Moscow). For each tomograph, the average weekly number of head and body examinations and the values of dose-length product for these areas were assessed, taking into account the number of multiphase examinations. The obtained workload values turned out to be one or two orders of magnitude higher than those currently used in calculating shielding. Based on the results of the study and literature data, the work proposes a new approach to calculating shielding in computed tomography rooms, based on the value of measured dose-length product during the examination and allowing to take into account the specifics of the operation of the device.

Keywords

• computed tomography
• shielding calculation
• relative scatter coefficients
• workload