Keywords:
Radiation physics, Computer applications, Radioprotection / Radiation dose, Digital radiography, Conventional radiography, CT, Dosimetry, Physics, Computer Applications-3D, Dosimetric comparison
Authors:
A. S. L. Dedulle, N. Fitousi, Z. Zeppelin, V. Petit, G. Zhang, J. Jacobs, H. Bosmans; Leuven/BE
DOI:
10.1594/ecr2018/C-2349
Methods and materials
In this study,
we have calculated dose conversion factors from voxel models made from the Computed Tomography (CT) scan of patients.
We opted for total body CT scans,
such that all organs of importance can theoretically be included in the study,
even though the current focus was chest PA imaging.
Voxel phantoms: Forty patients (20 female,
20 male) of different Body Mass Index (BMI),
who underwent a CT exam from head to thighs,
were selected.
The Water Equivalent Diameter (WED) [3] of every patient was calculated as the average WED over the central 20cm of the axial CT slices in the lung region (from top to bottom of lungs).
Their major radiosensitive organs were segmented: bones (for bone marrow and bone surface dose),
thyroid,
lungs,
breasts,
heart,
liver,
stomach,
colon,
kidneys,
bladder,
gonads,
uterus(F)/prostate(M),
skin,
muscle,
air inside the body and the remainder (Fig. 1 and Fig. 2).
Organ dose simulation: An in-house developed Monte Carlo (MC) framework (EGSnrc) built for cone-beam CT [4-5] was adjusted and configured for 2D radiography.
Commonly used chest PA examination parameters were determined from the dose monitoring system (DOSE by Qaelum,
Belgium),
in routine use in the university hospital of Leuven.
Organ dose conversion factors were generated for the typical,
clinically used x-ray spectra and standard radiographic parameters.
Statistics: A statistical program (GraphPad Prism, GraphPad Software Inc.
USA) was used to analyze and subsequently visualize the data.
Analysis was done separately for female and male patients.
Normality was tested and the influence of the BMI and WED on the organ dose conversion factors inside the field of view (red bone marrow,
thyroid,
lungs,
heart and breasts) was evaluated with two-tailed p-values with a confidence interval of 95% (p <0.05).