Abstract ID: 167 Assessing the CTDIVOL and SSDE from dose profiles in cylindrical phantoms of water equivalent materials

Abstract

The assessment of the Computed Tomography (CT) radiation output has become a challenge to researchers and technicians due to the rapid evolution of the technology incorporated in CT machines. To guarantee the correct performance and to avoid accidents in CT examinations, the novel CT units require the use of specific phantoms for dosimetry and imaging evaluations. Nevertheless, such phantoms are expensive or they are unavailable in the market. In this work, water equivalent materials produced in the Medical Physics and Radiation Dosimetry Group of the University of Sao Paulo [1] will be evaluated in order to demonstrate their use in phantom fabrication for dosimetry and imaging purposes. Dose profiles along the central and peripheral axis of cylindrical phantoms of water equivalent material were computed in order to assess the quantities: volume CT Dose Index ( CTDI vol ) and Size Specific Dose Estimate (SSDE). The CTDI vol and SSDE are used as CT radiation output and patient dose descriptors, respectively. Three water equivalent materials: H2O_1 (Propylene + Chloroethylene + Sodium hydroxide), H2O_2 (Propylene + Phosphorous acid + Sodium hydroxide) and H2O_3 (Polyethylene + Sodium hydroxide + Calcium Fluoride) were evaluated in this work. X-ray source models based on phase space files generated by Monte Carlo simulation for 80, 100, 120 and 140 kV. The X-ray source model was implemented following the technical specification of the GE Lightspeed Ultra CT machine (General Electric Company, Boston, USA) and it incorporates the anode self-attenuation, anode tilt and the bowtie filters for head and body examination. The CTDI vol was computed in a cylindrical phantom of 15 cm length and the SSDE was achieved varying phantom diameters of 5–40 cm. CTDI vol and SSDE results were compared with literature data for reference materials. Finally, the results of this work will be used as reference to guarantee the usefulness of the materials developed in the GDFM in the manufacture of simulators for CT quality control.