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

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).

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.

  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.

E relates radiation exposure to stochastic effects. The estimated value (E = 2.5±0.21 mSv), reveals that chest CT protocol used was optimized.