Abstract
Purpose : To investigate the discrepancy between effective diameter (dEFF) and water-equivalent diameter (dW) in size-specific dose estimate (SSDE) calculations for chest CT examinations.
Methods : This retrospective study analyzed 201 patients undergoing chest CT. The volumetric CT dose index (CTDIvol) was recorded for each case. Both dEFF and dW were calculated from the central axial image, with subsequent derivation of size conversion factors (fEFF, fW) and SSDE values (SSDEEFF, SSDEW). Patients were stratified into tertiles based on lateral chest diameter (dLAT): Group A (dLAT<32.955 cm), Group B (32.955-35.190 cm), and Group C (dLAT>35.190 cm). The comparison between different dLAT groups was conducted using the Friedman rank sum test. All statistical analysis was significant as P <0.05.
Results : The mean CTDIvol was 10.42 ± 0.44 mGy. Significant discrepancies were observed between dEFF and dW (t = -16.24, P < 0.001),
corresponding conversion factors (U = 5,030.50, P < 0.001), and SSDE values (U = 12,590.50, P < 0.001). Intergroup analysis revealed statistically significant differences across all parameters (ANOVA F = 134.000-357.249, all P < 0.001).
Conclusion : Water-equivalent diameter demonstrates superior accuracy over geometric measurements for SSDE calculation in chest CT, particularly for patient-specific dose optimization. These findings, while specific to GE scanners, highlight the clinical importance of attenuation-corrected metrics in radiation dose management.
Advances in knowledge : This study provides robust evidence for the feasibility and accuracy of attenuation-corrected dose calculations. The findings redefine personalized dosimetry paradigms, demonstrating that integrating inherent tissue attenuation variability significantly improves treatment planning reliability.