Determining organ doses from CT with direct measurements in postmortem subjects: Part 2-correlations with patientspecific parameters

Purpose: To generate empirical sets of equations that can be used to calculate patient-specific organ doses resulting from a group of computed tomographic (CT) studies by using data from direct dose measurements performed within a human body. Materials and Methods: Organ dose measurements were obtained in eight postmortem female subjects. A chest-abdomen-pelvis protocol was used for this study. The relationships among measured organ doses, body mass index, effective diameter (D_eff), and volume CT dose index (CTDI_vol) were investigated. Organ dose equations were developed by means of linear regression from organ dose data, with CTDI_vol and D_eff as variables, by using Pearson correlation coefficients and P values to determine correlation strength of fit. Measured organ doses were compared with corresponding size-specific dose estimates (SSDEs). Results: The central-section D_eff presented similar correlations with organ doses to those from D_eff measured at specific organ locations. The strongest correlations were observed between the central-section D_eff and CTDI_vol-normalized organ doses (R2: 0.478-0.941). The average of measured organ doses for each subject resulted in an average difference of only 5% from SSDE-calculated doses; however, individual organ doses differed from +31% to 261% from the calculated SSDE. Conclusion: The organ dose equations developed represent a method for organ dose estimation from direct organ dose measurements that can estimate organ doses more accurately than the calculated SSDE, which provides a less-specific patient dose estimate.