132 M . Keshtkar : Radioprotection 2024 , 59 ( 2 ), 131 – 137 to a doubling of the risk of leukemia ( Pearce et al ., 2012 ). Also , Meulepas et al . conducted a retrospective cohort study on 168,394 children nationwide and discovered a link between exposure to radiation from CT scans and an elevated risk of brain tumors ( Meulepas et al ., 2019 ).
Given these findings , it is crucial to adopt radiation dose reduction techniques and follow evidence-based imaging guidelines to minimize unnecessary radiation exposure and ensure the clinical benefits of CT scans outweigh the associated cancer risks in pediatric populations .
During the COVID-19 pandemic , our hospital faced a large number of CTscans for the diagnosis , screening , and monitoring of COVID-19 paediatric patients . In order to reduce paediatric radiation dose , we implemented a new chest CT protocol called COVID-19 Diagnosis CT protocol ( CD-CT ).
The objective of this study is to compare the radiation dose and the risk of cancer incidence associated with ionizing radiation in two chest CT protocols : namely , the routine chest CT ( RC-CT ) protocol and the CD-CT protocol .
2 Materials and methods
The study received approval from our institution ’ s ethics committee , and obtaining consent forms was not deemed necessary . This retrospective study recorded a total of 254 patients who underwent a chest CT examination with RC-CT protocol or CD-CT protocol from March 2020 to May 2022 . The patients were divided into three age groups : G1 (< 5 ), G2 ( 5 –< 10 ), and G3 ( 10 – 15 ). It should be noted that the CD-CT protocol was chosen for patients undergoing COVID-19 diagnosis , while the RC-CT protocol was used for other patients with the indications of mainly evaluation of infectious and lung diseases . Patient ’ s demographic data were acquired through the picture archiving and communication system ( PACS ). The matching between the two groups ( CD-CT protocol and RC-CT protocol for males and females separately ) was conducted based on an equal number of patients and effective diameter . The patient selection between the two groups was carried out in a way to match the effective diameter in the two groups .
To calculate the effective diameter of the chest , the middle slice of the scanning region was used and the anterior-posterior ( AP ) and lateral ( L ) distances were measured . The equation recommended by AAPM 204 was then used to calculate the effective diameter ( Medicine , 2011 ) as follow ;
effective diameter ¼ p ffiffiffiffiffiffiffiffiffiffiffiffiffiffi APL
2.1 Collection of CT dose parameters
All patients were imaged with a 16 slice CT scanner ( Somatom Emotion , Siemens , Germany ). The chest CT scanning range was set using a scout view from the lung apices to the lung bases . Table 1 shows CT scanning parameters of two protocols for three age groups . Slice thickness and nominal beam width were constant for all groups . Three tube potentials ( kVp ) were used : 80 , 110 , and 130 , manually based on the CT technologist ’ s experience . Lower tube current ( mAs ) was used for CD-CT protocol , and the CareDose 4D option was activated for all patients during
CT scanning . All the radiologists working at our institution have approved the image quality of both protocols based on the assessment of image noise in the CTDI phantom .
The values of volumetric CT dose index ( CTDIvol ), dose length product ( DLP ) and the parameters of two chest CT protocols were extracted from dose report page by looking back at the PACS .
In this study also size specific dose estimate ( SSDE ) was calculated by multiplying CTDI vol and a conversion factor provided in AAPM 204 report . The SSDE is a more accurate radiation dose metric for patients of different sizes compared to the CTDIvol alone , as it takes into account the patient ’ s size , which can affect the effective dose received during the CT scan .
2.2 Estimation of organ dose and effective dose
Organ doses ( mSv ) and effective dose ( mSv ) were estimated using the National Cancer Institute dosimetry system for CT ( NCICT ) software version 3.0 ( Lee et al ., 2015 ). Organ doses were calculated for organs in the field of scanning range such as thyroid , esophagus , lung , breast and stomach by employing a Monte Carlo simulation and an International Commission on Radiological Protection ( ICRP ) standard pediatric phantom ( Lee et al ., 2015 ).
2.3 Estimation of cancer incidence risk
Estimation of cancer incidence risks were conducted according to the Biological Effects of Ionizing Radiation ( BEIR ) VII report ( Council , 2006 ). The models presented in the BEIR VII report take into account a range of factors that can influence the risk of cancer , the age and gender of the exposed individual , and the dose . The report also provides estimates of the risks associated with different types of cancer , including solid tumors and leukemia .
Cancer risks were calculated for different organs , including thyroid , lung , and breast .
2.4 Statistical analysis
The statistical analysis was performed using SPSS software ( version 23 ), with mean and standard deviation ( SD ) used to express all values . Furthermore , the Mann – Whitney test was employed to compare the means of continuous variables between thetwo groupsdue tothe non-normality of the data , asassessedby the Kolmogorov – Smirnov test . Statistical significance was interpreted as differences with a p-value less than 0.05 .
3 Results
Table 2 shows demographic data and values of effective diameter for the two groups of the patients . The number of patients in the two protocols according to gender was equal to facilitate a better matching process . The age of patients ranged from 2.7 ± 0.9 years in the male CD-CT protocol group to 13.0 ± 1.7 years in the female CD-CT protocol group . There were no statistical differences in terms of effective diameter between the two protocols for all age groups ( P > 0.05 ).