CT Output Dose Performance-Conventional Approach versus the Dose Equilibrium Method

• 作者: Ahmad Albngali Andy Shearer Brendan Tuohy Niall Colgan Wil van der Putten
• 来源期刊: 医学物理学、临床工程、放射肿瘤学(英文)
• 学科: 医学
• 关键词: Computed Tomography DIXON Method FARMER Chamber CT DOSIMETRY
• 年，卷（期）: 2018,（1）
• 页码范围: 15-26
• 页数: 12页
• 分类号: R73

摘要

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.