Application of a Tandem system for HVL evaluation in computed tomography

Abstract

Computed tomography (CT) is a method of imaging used for the diagnosis and treatment of diseases. Different from the conventional diagnostic radiology equipment, where the test for the determination of the half value layer (HVL) is recommended, in CT equipment due to its geometry, the determination of the HVL is a difficult task and is usually only provided by the manufacturer. The effective energy of a beam is determined by definition, by means of HVL determination. When HVL values are not easily determined, as in the case of CT, it is possible to evaluate the effective energy of the beam through a system consisting of the use of different energy dependent dosimeters, where the ratio between the calibration curve responses in energy can provide the effective energy of the beam (Tandem system). The system used in this work for the evaluation of HVL in computed tomography is composed of groups formed by an ionization chamber of the pencil-type and cylindrical absorber layers of aluminum and Polymethyl methacrylate (PMMA).