Determining Organ Doses from CT with Direct Measurements in Postmortem Subjects: Part 2--Correlations with Patient-specific Parameters.

Abstract

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. 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). 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 (R(2): 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 -61% from the calculated SSDE. 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.