Doses Used in Fluoroscopic Lumbar Epidural Injections Overestimated

Fluoroscope-reported values may overestimate total patient entrance dose-area product used in lumbar epidural injections, according to a recent study published in Pain Medicine.

To determine the extent of system inaccuracies and table attenuation on fluoroscope-reported dose values, researchers gathered acquisition data on 46 patients who underwent fluoroscopy-guided lumbar injections within the L1-S1 vertebral region.

According to system-reported data provided by the c-arm used for all injections, exposure-in-air values were accurately reported with errors of less than 8% across all measured kilovoltage settings.  The researchers found that transmission factors for table and support attenuation varied appreciably with kilovoltage, with measured transmission factors of 66% to 76%. Histogram data were shown to shift and tighten toward lower dose-area product values after applying corrections.

The average uncorrected dose-area product value for anteroposterior (“with table”) views was 43% higher than corrected values (P <.01), and there was an average difference of 34% between corrected and uncorrected dose-area product when analyzing the average dose-area product for the whole procedure (P <.01).

Demographic data and physical measurements were used to explore additional trends in total exposure. Moderate correlation was established between body mass index and corrected dose-area product across the study population and between dose-area product and anteroposterior thickness, but no correlation for lateral (“without table”) thickness.

Study limitations include a small sample size and the examination of a single type of procedure.

“Caution should be taken when deciding how to best use system-reported [dose-area product] values for any comparison across procedures, equipment, and clinics,” concluded the study authors.

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Mann SD, Joshi A, Shonyo M, et al. Improved dose estimates for fluoroscopically guided lumbar epidural injections [published online September 12, 2018]. Pain Med. doi: 10.1093/pm/pny172