59. Planar average equilibrium dose during CT exams with Optima CT660 CT System

• Published in: Physica medica 2018-12, Vol.56, p.100-100
• Main Authors: Ordonez, P.L., Haddad, K.M., Strigari, L., Guerrisi, A., Bruzzaniti, V.
• Format: Article
• Language: English
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2018.04.069

The planar average equilibrium dose Deq (in air kerma terms) is a new CT dose index which is analogous to the CTDIvol, but considers the contribution of radiation scattered beyond the 100-mm range of integration along z [1]. The purpose of this work was to measure Deq in Abd/Pelvis and Chest scans using the Optima CT660 System for medium adult patient [2] and to compare them with the corresponding CTDIvol. The measurements were performed in agreement with the AAPM Task Group 111 Report [1], i.e. by using a small volume ionization chamber (Farmer-type) positioned in a phantom long enough to establish dose equilibrium at the location of the chamber. The cumulative exposure for different z-scan lengths (L), were recorded at the longitudinal centre of the central and peripheral axes of the phantom. An inter-calibration procedure, which uses the same CT beam of the scans and a pencil type ionization chamber, was implemented to obtain an adequate NK calibration factor. To perform the scans of reference, we chose the Abd/Pelvis CT Protocol [2] for Optima CT6602. The uncertainty of measurements was assessed following the GUM [3] recommendations. The Figures show the cumulative dose at z = 0 vs L for the central (red curves) and peripheral axes (blue curves) for different tube currents. The (Deq vs. CTDIvol) in mGy units were; (17.1 vs 13.5) for the Abd/Pelvis scans and (6.4 vs 5.1) for the Chest scans.▪ CTDIvol underestimates the dose by aprox. 27%, CI (25, 29) at P(68%).