Date(s) - 06/05/2013
Computed tomography has allowed for great advances in the field of diagnostic imaging. However, this progression has not ensued without careful attention to the radiation dose associated with its use. There remains a critical need to accurately assess organ doses resulting from these procedures. The ultimate goals of this research study were: first, to develop sets of empirical equations that can be utilized to calculate patient-specific organ doses for a group of commonly performed CT exams, and second, to investigate the effects of ultra-helical acquisition mode on organ doses.
Both of the aforementioned goals were accomplished with the use of a standardized direct organ dose measurement methodology utilizing optically stimulated luminescent dosimeters (OSLDs) and performing the measurements on cadaveric subjects in lieu of actual patients. The OSLDs were placed on the skin and lens of the eye, and within the following organs: thyroid, brain, lungs, breasts, liver, stomach, small intestine, large intestine, uterus, and ovaries. A variety of clinically-accepted CT protocols was examined, including chest (C), abdomen (A), pelvis (P), CAP, 3-phase liver, pulmonary embolism, trauma, head, CTA head, and brain perfusion protocols.Average organ doses for all body protocols examined ranged from 2 mGy to 84 mGy, with the maximum dose resulting from the three-phase liver protocol and largest detector configuration, 0.5 mm x 160. Organ dose measurement for the head protocols resulted in a dose range of 16-299 mGy, with the highest dose resulting from the lens dose of a brain perfusion protocol. Overall, organ doses were shown to increase with the size of the detector configuration.
Average organ doses from 8 cadaveric subjects and five primary protocols were compiled and normalized by the exam CTDIVol. Equation sets were derived from correlations between these dose conversion coefficients and the central effective diameter of each subject.
These equations present a novel and innovative method for organ dose estimation due to their origin in direct organ dose measurements. With this research, the first step has been made in acquiring the ability to calculate patient-specific organ doses in computed tomography, and in turn more appropriately estimate the risk from CT studies.