Estimation of effective dose using the dose length product in chest computed tomography procedures

Background: Approximation of radiation risks in computed tomography (CT) requires knowledge of specific organ doses. A Rando phantom and thermoluminescent dosimeters (TLDs) provide a proxy for in-vivo measurements. In this study, measured chest CT doses were used to calculate dose length product (DLP), a dosimetric needed for estimation of effective dose (E). Method and Materials: Ninety-five calibrated TLDs embedded at peripheral and central positions of Rando phantom chest slice measured chest CT dose during imaging using Phillips Brilliance 64-slice CT scanner. Three measurements were conducted each with new TLDs. Irradiated TLDs were read with a Harshaw TLD reader (Model 3500). One-way ANOVA test verified statistical significance of TLD measurements. TLD doses were used to calculate chest CT dose given as dose length product (DLP), a product of chest slice CT dose measured by volumetric CT dose index (CTDIv) multiplied by scan length. Consequently, E was calculated as the product of DLP and k, an adult chest conversion factor published by International Commission on Radiological Protection Publication 103. Results: Differences in mean TLDs measurements were statistically significant (p=0.032). The mean chest slice peripheral and center doses were 3.61 ± 0.6 and 4.60 ± 0.31 mGy respectively. Adult chest CT dose was 178.8 ± 15 mGy. E was estimated as 2.5 ± 0.21 mSv. It is than the range (5.6 – 9.3 mSv) found in literature. Conclusion: E relates radiation exposure to stochastic effects. The estimated value (E = 2.5±0.21 mSv), reveals that chest CT protocol used was optimized.