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Description
Introduction: Computed tomography uses computed tomography dose index to estimate patient’s dose. However, it only accounts for scanner dose output using a reference phantom of unvarying size and content rather than patient`s morphology. The size specific dose estimate accounts for scanner dose output and patient size. There is no current documented diagnostic reference level established based on size metric in the study location. Hence no report of estimated patient doses based on size which necessitate this study to ensure that patient doses during CT are consistent with patient sizes not just machine reported doses.
Objectives of the Study: To determine the typical value and proposed local DRL based om size specific dose estimate (SSDE) for routine adult CT examination of head, thorax and abdomen.
Method: A retrospective, cross-sectional study was adopted for this study. Dose values was obtained from the visual display unit of the CT scanners. The SSDE is calculated using American association of physicians in medicine established formular. SSDE = CTDIvol x f. Water equivalent diameter was used as the conversion factor (f).
Result: A total of 110 CT examinations were retrospectively analyzed, comprising 40 head, 30 thorax and 40 abdomen scans. The median SSDE (75th percentile) and CTDIvol (75th percentile) for head: 56.3mGy (56.3mGy) and 62.5mGy (62.5mGy); thorax: 7.1mGy (8.8mGy) and 5.2mGy(6.6mGy) respectively; abdomen: 11.0mGy ( 13.6mGy) and 7.8mGy ( 9.2mGy) respectively. A Related Wilcoxon Signed Rank Test revealed a statistically significant difference between CTDIvol and SSDE in all region studied.
Conclusion: This study demonstrates the critical importance of implementing SSDE for accurate patient dose estimation in CT. The significant differences found between CTDIvol and SSDE confirm that CTDIvol can both overestimate and underestimate patient dose depending on the body region and patient size.