Dose reference level based on size-specific dose estimate (SSDE) and feasibility of deriving effective body diameter using tube current and time product (mAs) for adult chest and abdomen computed tomography (CT) procedures

Autor: T Amalaraj, Jeyasingam Jeyasugiththan, Duminda Satharasinghe, A S Pallewatte
Rok vydání: 2023
Předmět:
Zdroj: Journal of Radiological Protection. 43:011505
ISSN: 1361-6498
0952-4746
Popis: This study aimed to establish dose reference level (NDRL S S D E ) based on size-specific dose estimate (SSDE) derived using effective diameter ( D e f f ) for adult chest and abdomen computed tomography (CT) procedures and to explore the feasibility of driving D e f f using the product of tube current and time (mAs). In this retrospective study, dose data, scan parameters and patient body dimensions at the mid-slice level from 14 CT units (out of 63 total) were extracted. Additionally, the mAs values of the axial slice at the same z-location where the diameter measurements were made (mAs z ) were recorded. Pearson’s correlation (r) analysis was used to determine the relationship of D e f f with patient BMI, weight, and mAs z . The NDRL S S D E for the chest and abdomen were 9.72 mGy and 13.4 mGy, respectively. The BMI and body weight were less correlated (r = 0.24 and r = 0.33, respectively) with D e f f . The correlation between mAs z and D e f f was considerably strong (r = 0.78) and can be used to predict D e f f accurately. The absolute dose differences between SSDEs calculated using the AAPM–204 method and mAs z was less than 1.1 mGy (15%). Therefore, mAs z is an efficient parameter to derive D e f f . Further, the direct conversion factors to estimate SSDEs at different locations along the z-direction in the scan region from corresponding mAs and CTDI v o l were calculated. The NDRL S S D E suggested in the present study can be used as a reference for size-dependent dose optimisation in Sri Lanka, and existing NDRL based on CTDI v o l underestimate the average adult CT dose by 36.0% and 39.7% for chest and abdomen regions respectively. The results show that using mAs z to determine SSDE is a simple and practical approach with an accuracy of 95% and 85% for abdomen and chest scans, respectively. However, the obtained linear relationship between D e f f and mAs is highly dependent on the ATCM technique and the user-determined noise levels of the scanning protocol. Finally, the phantom study resulted in the strongest correlation (r = 0.99) between the D w z and mAs z , and the prediction of patient size would be more precise than D e f f method.
Databáze: OpenAIRE
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