Keywords:
Radiation physics, Radioprotection / Radiation dose, CT, CT-Quantitative, Cone beam CT, Physics, Radiation safety, Education, Quality assurance, Education and training
Authors:
A. Albngali, A. Shearer, W. van der Putten, B. Tuohy, N. Colgan; Galway/IE
DOI:
10.1594/ecr2018/C-1445
Aims and objectives
Current output dose measurement in CT is based on the Computed Tomography Dose Index (CTDI) .
The CTDI method utilizes a 10-cm long pencil ionization chamber placed in a 16-cm long Perspex phantom at 5 different sites.
The CTDI dose estimation is performed using a single rotation for each reference site and excluding the contribution of radiation scattered beyond the 100-mm range of integration along z.
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. The “Dixon” method(1,2) is a new technique which more accurately characterizes the dose profile from a modern CT scanner. It uses a small volume farmer chamber to directly measure the cumulative dose D(x) at any point by scanning a sufficient length of phantom to produce dose equilibrium at the centre.
The purpose of this study is to characterize an in house “Dixon” phantom design using a number of clinical scan sequences,
and determine the accumulated dose in a water phantom,
determine 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 Dixon phantom measurements .
All dose measurements were independently verified with TLD measurement.