Author(s)

Ahmad Albngali^1*, Andy Shearer¹, Wil van der Putten^1,2, Brendan Tuohy^1,2, Niall Colgan^1,2

¹Department of Physics, National University of Ireland, Galway, Ireland.
²Department of Medical Physics and Clinical Engineering, Galway University Hospitals, Galway, Ireland.

Current output dose measurement in CT is based on (CTDI). The conventional methodology of CT dosimetric performance characterization is not appropriate to modern CT scanners with helical scanning modes, dose modulation, array detectors and multiple slice planes or cone-beam irradiation geometries. AAPM TG 111 report recognizes the shortfall of the CTDI methods and recommends a new technique that more accurately characterizes the dose profile from modern CT scanners, which utilizes a short conventional ion chamber rather than a pencil chamber. We developed and characterize a in-house phantom design using a three separate anatomical regions of clinical scan sequences (Head, chest and abdomen), and determined the equilibrium dose in our dose equilibrium phantom, measured if the attenuation of the beam is the equal to that of CTDI Perspex phantom and compare CTDI dose estimations using a standard pencil chamber to the dose equilibrium phantom measurements. This methodology allows measurements of the accumulated dose for any clinical scan length and allowing measurement of the equilibrium dose. Using the new methodology, we determined that the CTDI approach can underestimate the dose by 25% to 35% and all of our dose values from the water phantom and farmer chamber were independently verified with TLD measurements.

Computed Tomography, Dixon Method, Farmer Chamber, CT Dosimetry

Albngali, A. , Shearer, A. , van der Putten, W. , Tuohy, B. and Colgan, N. (2018) CT Output Dose Performance-Conventional Approach versus the Dose Equilibrium Method. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 7, 15-26. doi: 10.4236/ijmpcero.2018.71002.