Local diagnostic reference levels (drls) for paediatric contrasted abdominal computed tomography (ct) examinations for nephroblastoma

Abstract

Computed tomography (CT) has become essential to paediatric radiology with the ongoing technological developments, and has been established as an important part of the diagnostic procedure (Hojreh, Weber & Homolka, 2015:1574). However, paediatric CT poses a particular concern, since paediatric patients have a high risk from radiation (Järvinen, Seuri, Kortesniemi, Lanjunen, Hallinen, Savikurki-Heikkilä, Laarne, Perhomaa & Tyrväinen, 2015:86). Therefore, it is important to pay attention to the justification and optimisation of paediatric CT examinations (Järvinen et al., 2015:87). An essential part of optimisation is developing diagnostic reference level (DRL) values (Saravanakumar, Vaideki, Govindarajan, Devenand, Jayakumar & Sharma, 2016:342). The International Commission on Radiological Protection (ICRP) describes DRL values as a form of investigation levels applied to an easily measured quantity (Saravanakumar et al., 2016:342). Furthermore, the ICRP (2017:31) indicated that DRL values are not dose limits and are not based on individual patients but rather on a specific group of patients. According to hospital reports, paediatric patients who presented for abdominal CT examinations at the participating hospitals were most likely to have nephroblastoma (Lesetja, 2021). It was found through a literature evaluation that no documented paediatric local DRL (LDRL) values existed for CT examinations to investigate and stage nephroblastoma in South Africa. The absence of established clinical indication-based paediatric LDRL values in South Africa limits the ability to identify unusually high dose levels, and ensure optimal radiation protection during contrast-enhanced abdominal CT examination of paediatric patients who present with nephroblastoma. The aim of the study was to establish paediatric LDRL values for contrast-enhanced abdominal CT examinations to diagnose and stage nephroblastoma cases. To achieve the aim of this study, three objectives were pursued: (1) to develop paediatric LDRL values that are linked to the patient’s weight and age for contrast-enhanced abdominal CT examination for nephroblastoma cases; (2) to compare LDRL values calculated, using weight versus effective diameter of the patient, and (3) to compare the clinical indication-based LDRL values with other internationally published clinical indication-based LDRL values. The study followed a descriptive research design, and data from paediatric patients who underwent CT abdominal examination to diagnose nephroblastoma from 1 January 2018 to 31 December 2021 were collected retrospectively. In this research study, the researcher used a structured data recording document to descriptively gather dose information from the dose reports on the picture archiving and communication system (PACS) or CT console and the CT register file. Thereby, paediatric LDRL values for contrast-enhanced abdominal CT examinations based on the clinical referral of suspected or confirmed nephroblastoma were established. A structured data recording document was used to obtain the volume computed tomography dose index (CTDIvol), dose length product (DLP), clinical indication, anterior-posterior (AP) dimensions, lateral (LAT) dimensions, effective diameter, age, and weight of the patients. The size-specific dose estimates (SSDE) parameters were calculated using methods provided by the American Association of Physicists in Medicine (AAPM) Report 204. The target population of this study consisted of paediatric patients who presented with nephroblastoma for contrast-enhanced abdominal CT examinations at the participating hospital. The sample size of paediatric patients who formed part of this research study was 120 patients for contrast-enhanced abdominal CT examination. The patients were categorised into five age groups (group 1 [<1 month (M)); group 2 [1M to <4 years (Y)); group 3 [4Y to <10Y); group 4 [10Y to <14Y), and group 5 [14Y to <18Y)) and five weight categories (group 1 [0kg - <5kg), group 2 [5kg - <15kg), group 3 [15kg - <30kg), group 4 [30kg - <50kg) and group 5 [50 kg to <80 kg)), as suggested by the ICRP (2017:93). Furthermore, the sample was also grouped according to five effective diameter groups (group 1 [<13 cm); group 2 [13 cm to <16 cm); group 3 [16 cm to <20 cm); group 4 [20 cm to <24 cm), and group 5 [<24 cm)). The effective diameter was calculated from the square root of the product of the patient’s AP and LAT dimensions’ measurements as suggested by ICRP (2017:97). A minimum of 20 patients for each group was needed to develop LDRL values for this study based on the 75th percentile. The data from the age, weight or effective diameter groups with fewer than 20 patients to establish LDRL values for nephroblastoma were excluded. Therefore, LDRL values were established only for • two weight groups: weight group 2 [5kg - < 15kg), weight group 3 [15kg - < 30kg), three age groups: age group 2 [1M to <4Y), age group 3 [4Y to <10Y) and age group 4 [10y to <14y), and • two effective diameter groups: effective diameter group 2 [13 cm to <16 cm) and effective diameter group 3 [16 cm to <20 cm). The paediatric LDRL values (75th percentile) based on the CTDIvol ranged from 2.7–7.1 mGy, 2.7–3.5 mGy, and 2.8–6.5 mGy for age groups, weight groups and effective diameter groups, respectively. The DLP, 75th percentile paediatric LDRL values for age groups ranged from 98.7–367.9 mGy.cm, 95.7–162.6 mGy.cm for weight groups, and 111.8–325.9 mGy.cm for effective diameter groups. The LDRL values (75th percentile) based on the SSDE parameters (AP, LAT, SUM and effective diameter) ranged from 5.6–12.8 mGy, 5.6–6.9 mGy and 5.9–12.2 mGy for age groups, weight groups and effective diameter groups, respectively. Based on a 95% confidence limit calculated on the 75th percentile, a significant difference was detected between CTDIvol and SSDE parameters, indicating that both dose quantities had different effects on radiation exposure. Since the CTDIvol provides only information about the scanner's output, it cannot estimate size-specific patient doses (AAPM, 2011:2). Therefore, according to AAPM (2011:18), the SSDE should be used as it incorporates corrections for patient sizes. The DLP, CTDIvol, and SSDE parameters did not correlate with weight in weight group 2 (5 kg to <15 kg). The DLP, CTDIvol, and SSDE parameters significantly correlated with weight group 3 (15 kg to <30 kg). The ICRP (2017:93) and European Commission (2018:32) stated that patient weight is the most reliable factor associated with the DRL quantity. Therefore, weight should still be used for categorising, as the ICRP (2017) suggested. The LDRL values calculated using weight were compared with the effective diameter of the patient. The weight and effective diameter LDRL values were comparable, and Spearman’s coefficient correlation indicated a significant correlation between patient weight and effective diameter. Therefore, the weight (kg) or the effective diameter (cm) can be used to categorise the patients. However, the ICRP (2017:97) recommended that the effective diameter should be considered in addition to weight during the development of DRL values. Unlike weight and age, effective diameter represents dimensional measurement at a specific cross-sectional image, while weight and age represent the area being scanned (Cook, Chadalavada & Boom, 2013:2). This study's clinical indication-based LDRL values were also compared with the internationally published LDRL values. No studies could be found in South Africa or internationally that have developed LDRL values, specifically for nephroblastoma in paediatric patients. The LDRL values for paediatrics developed in this study were somewhat lower than most DRL values found in various studies, except those by Hwang, Choi, Yoon, Ryu, Shin, Kim, Lee, You and Park (2021) and Almén, Guðjónsdóttir, Heimland, Højgaard, Waltenburg and Widmark (2022). The radiation dose accumulated by paediatric patients involved in this study was lower due to the number of scan sequences and the use of automatic tube current modulation (ATCM) and iterative reconstruction (IR) algorithms. The established LDRL values in this study will contribute as a guide to optimise the radiation dose received by paediatric patients for nephroblastoma. The findings of this study further support the idea that the effective diameter groups, together with the SSDE dose quantity, should be used to develop paediatric DRL values, as suggested by ICRP (2017) and AAPM (2011).