Evaluation of absorbed dose to brain in patients undergoing head and neck helical CT based on AAPM report 293.

Abstract

This study used AAPM Report 293 to estimate absorbed doses (EADs) from head and neck CT examinations in 100 patients (ages 18-90), leveraging its superior accuracy over Report 220. The study used data from a diagnostic CT scanner of model Canon Aquilion Lightning 16-row 32-slice, between years 2022 to 2024, with IndoseCT version 20b software to extract parameters, such as volumetric CT dose index (CTDI_Vol), dose length product (DLP), X-ray tube current (mAs), X-ray tube voltage (kVp) and Size Specific Dose Estimation (SSDE) based on water equivalent diameter (D_w). Two IndoseCT methods were employed: Z-axis Slice Number technique for D_w and Z-axis Slice range technique for EAD. A correlation analysis using Pearson Correlation Coefficient (PCC) and Principal Component Analysis (PCA) investigated relationships between CT dose and patient size parameters. The analysis was conducted using Microsoft Excel software embedded with XLSTAT 2024 version. Results showed CTDIvol values were higher than SSDE in most age groups, except 40-59 and 70-79 years. EADs ranged from 29.21 ± 8.12 mGy for (18-30) to 33.07 ± 5.81 mGy for (≥ 30) age groups. Conversion factors (CF) were varied, with notable impact from the 70-79 age group. this study found similar trends in CTDIvol to SSDE conversion factors (CF) as past work, with a mean CF < 1 indicating slight underestimation of radiation dose (SSDE). Notably, by including the 70-79 age group, CF can be shifted from < 1 to > 1; this suggests that patient size in the 70-79 age group may require protocol optimization.