Purpose:
Water equivalent diameter (WED) is related to the computed tomography (CT) number. Lung lesions change the tissue attenuation properties in the COVID-19 patients. Thus, these lesions can change the CT number and affect the WED, conversion factors (CFs), and size-specific dose estimation (SSDE). We evaluated the effect of lung infection on the radiation dose in the CT scans of COVID-19 patients.
Methods:
One hundred eighty-six chest CT scans of adult COVID-19 patients were obtained from PACS under a retrospective study. All patients were categorised into five categories based on total severity score (TSS). The effective
diameter (Deff), WED (Dw), conversion factor, CTDIv, and SSDE are calculated for all slices based on AAPM TG-220. One-way ANOVA test following Tukey’s post hoc test is used to compare the mean of Deff, CFeff, Dw, CFw, (SSDEw ) and computed tomography dose index (CTDIv) among all pairwise TSS groups. The correlation among mentioned parameters with TSS is determined by the Spearman’s correlation coefficient.
Results:
Although there was no difference for Deff and CF among all TSS groups but the Dw, CFs, and PDIF were significantly higher for COVID-19 patients than healthy cases. Furthermore, our study showed that TSS is correlated with Dw
(r = 0.29, P-value = 0.001), and CFs (r = - 0.29,
P-value = 0.001). (SSDE_w ) was significantly different among all pairwise groups when fixed tube current (FTC) was used. We found A significant difference for (SSDEw ) (On-ATCM) between healthy-moderate (P-value = 0.006) and healthy-mild (P-value = 0.04) TSS groups.
Conclusion:
Lung lesions change the Dw and CFw, which can affect the patient’s radiation dose in COVID-19 paients. Increasing TSS causes a decrease in CFw and (SSDEw ) when low-dose protocol with FTC was performed. Moreover, in some TSS groups, the lung lesions can affect the (SSDEw) when ATCM is used. It seems some pathologies can affect the cancer risk from CT scan exposure.