Validation of calculation algorithms for organ doses in CT by measurements on a 5 year old paediatric phantom

Abstract

Many organ dose calculation tools for computed tomography (CT) scans rely on the assumptions: (1) organ doses estimated for one CT scanner can be converted into organ doses for another CT scanner using the ratio of the Computed Tomography Dose Index (CTDI) between two CT scanners; and (2) helical scans can be approximated as the summation of axial slices covering the same scan range. The current study aims to validate experimentally these two assumptions. We performed organ dose measurements in a 5 year-old physical anthropomorphic phantom for five different CT scanners from four manufacturers. Absorbed doses to 22 organs were measured using thermoluminescent dosimeters for head-to-torso scans. We then compared the measured organ doses with the values calculated from the National Cancer Institute dosimetry system for CT (NCICT) computer program, developed at the National Cancer Institute. Whereas the measured organ doses showed significant variability (coefficient of variation (CoV) up to 53% at 80 kV) across different scanner models, the CoV of organ doses normalised to CTDIvol substantially decreased (12% CoV on average at 80 kV). For most organs, the difference between measured and simulated organ doses was within ±20% except for the bone marrow, breasts and ovaries. The discrepancies were further explained by additional Monte Carlo calculations of organ doses using a voxel phantom developed from CT images of the physical phantom. The results demonstrate that organ doses calculated for one CT scanner can be used to assess organ doses from other CT scanners with 20% uncertainty (k = 1), for the scan settings considered in the study.

Organ doses evaluation for chest computed tomography procedures with TL dosimeters: Comparison with Monte Carlo simulations

“…17 The organ dose calculated from the software has been extensively tested by measurements. 44,45 Comparison results are presented along with the percent differences between experimental (D exp ) and simulated (D sim ) values per organ, as follows:…”

“…Percent differences reported by these authors are within 13% for organs that were within the scan range and the authors considered measured and simulated results to be in good agreement. In the study conducted by Dabin et al, 44 16 and they were calibrated using the same CT scanner used for the measurements (thus the same X ray beam), therefore it was not necessary to correct for the energy dependence.…”

Conversion factors to derive organ doses for canine subjects undergoing CT examinations

“…Another approach uses computer calculations where X‐rays emitted from CT machines and the human anatomy are simulated by a statistical tool called Monte Carlo radiation transport. We adopted a 3D Monte Carlo simulation model of a reference CT scanner (Sensation 16, Siemens Healthineers, Munich, Germany), previously published elsewhere 12 and experimentally validated, 17–19 in which detailed technical features are modeled based on the data obtained from the manufacturer. We used three different X‐ray energies: 80, 100, and 120 kV.…”

Avaliação de doses em órgãos em procedimentos de tomografia computadorizada utilizando dosímetros TL e OSL

“…Percent differences reported by these authors are within ±13% for organs that were within the scan range and the authors considered measured and simulated results to be in good agreement. In the study conducted by Dabin et al (2016), the authors performed organ dose measurements in a 5-year old anthropomorphic phantom for five different CT scanners from four manufacturers. The authors measured absorbed doses to 22 organs by directly applying TLDs inside the organs of the phantom for head-to-torso acquisitions.…”