Relationship between specific organ doses and volumetric CT dose indices in multidetector CT studies

Organ doses are useful for estimating radiation doses to patients. However, it is impossible to determine specific organ doses for each patient. The aim of this study was to examine the relationship between specific organ doses and volumetric CT dose indices (CTDIvols) in multidetector CT studies to estimate specific organ doses in each patient. Radiophotoluminescent glass dosimeters were placed at locations corresponding to specific organs of an anthropomorphic phantom. Thereafter, the phantoms were examined with respect to various imaging ranges and protocols, including cranial, thoracic and abdominal acquisitions using a 64-section multidetector CT. Concurrently, we recorded the mean CTDIvol for each acquisition range. In the cranial acquisition, the displayed mean CTDIvol was 69.0mGy, and the absorbed doses for brain and intra-ocular lenses were 57.2±2.6 and 57.1±3.0mGy, respectively. In the thoracic acquisition, the displayed mean CTDIvol was 16.3mGy, and the absorbed doses for breast and lung were 19.1±6.4 and 31.7±2.2mGy, respectively. In the abdominal acquisition, the displayed mean CTDIvol was 21.6mGy, and the absorbed doses for stomach and colon were 28.2±6.1 and 28.0±8.6mGy, respectively. The displayed mean CTDIvols overestimated the specific organ doses in the cranial acquisition and underestimated them in the thoracic and abdominal acquisitions. However, the approximate specific organ doses may be estimated by multiplying the displayed mean CTDIvols with a conversion factor for each organ.