Congress:
EuroSafe Imaging 2019
Keywords:
Radioprotection / Radiation dose, Radiation physics, Paediatric, Action 5 - Performance indicators for radiation protection management, Action 4 - Dose management systems, Action 2 - Clinical diagnostic reference levels (DRLs), Digital radiography, Diagnostic procedure, Dosimetric comparison
Authors:
C. Polito, V. Cannatà, L. Di Chiara, B. Cassano, T. Insero, P. Toma, A. Magistrelli, M. Longo, E. Genovese
DOI:
10.26044/esi2019/ESI-0087
Description of activity and work performed
This study has been conducted over a period of 2 months in the Neonatal Intensive Care Unit of Bambino Gesù Children Hospital.
As suggested by European Guidelines on DRLs for Paediatric Imaging [2],
patients have been grouping in different weight classes (class 1 includes newborn having a weight < 5 Kg,
class 2 applies to infants with weight varying from 5 Kg to 15 Kg).
The study has involved 135 infants (92 in class 1 and 43 in class 2) undergoing chest X-ray examinations.
In the study only anterior-posterior (AP) images have been taken into account for DAP and effective dose analysis.
Relevant parameters like DAP,
peak tube voltage and tube current have been recorded during the examination.
Effective and organ doses have been calculated using PCXMC,
a PC-based Monte Carlo code able to assess organ doses in medical X-ray examinations [3].
PCXMC allows to calculate doses for 29 organs and the resultant effective dose to neonates according to the International Commission on Radiation Protection (ICRP) Report 103 tissue weighting factors [4].
It is worth to note that the defined field size borders used for PCXMC simulations refers to the effective field extracted from the DICOM image of each examination.
Box plot in Figure 1 depicts the median DAP and the interquartile range of the presented data (compared using Student's t-test with P < 0.05).
As expected,
median DAP value is higher for class 2.
Interquartile range are rather wide and there are some DAP outliers for the same weight class.
This is probably due to the absence of a defined protocol that makes the procedure operator dependent.
Exact values are given in Table 1.
In order to facilitate the comparison between our data and literature values,
the table also shows an overview of other recent studies.
The effective doses have been calculated for AP chest examinations for both weight classes and values are shown in Table 2 compared to the ones of other studies.
Furthermore,
as expected,
the study confirmed a linear correlation between DAP (device output) and effective dose (simulation output),
as shown in Figure 2,
with an R2of 0.8 and 0.7 for class 1 and 2 respectively.
The linear fit of E as function of DAP resulted in conversion coefficient of 1.6 mSv Gy-1 cm-2 (class 1) and 1.18 mSv Gy-1 cm-2 (class 2).
Moreover,
the mean organ doses have been investigated for both weight classes.
The calculated mean dose values related to the organs receiving considerable amounts of radiation doses for chest examinations are presented with the histogram of Figure 3.
A linear fit of the equivalent doses as function of DAP has been performed for the most irradiated organs.
Table 3 shows the DAP value for each weight class,
the organ dose resulting from simulations (mean value) and the conversion coefficient (CF) between DAP and organ dose for thoracic organs in mSv Gy-1 cm-2and the resulting R2.
In this way it is possible to calculate the organ dose from DAP using appropriate conversion coefficient,
although somewhere with a weak correlation.