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.
Reference
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
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