Kerma Area Product Method for Effective Dose Estimation During Lumbar Epidural Steroid Injection Procedures: Phantom Study

The purpose of this study was to derive from the kerma area product the dose conversion coefficient for estimating the effective dose for lumbar epidural steroid injection procedures. A mobile fluoroscopy system was used for fluoroscopic imaging guidance of lumbar epidural steroid injection procedures. For acquisition of organ dose measurements, 20 diagnostic metal oxide semiconductor field effect transistor detectors were placed at each organ in an anthropomorphic phantom of a man, and these detectors were attached to four mobile metal oxide semiconductor field effect transistor wireless bias supplies to obtain the organ dose readings. The kerma area product was recorded from the system console and independently validated with an ion chamber and therapeutic x-ray film. Fluoroscopy was performed on the phantom for 10 minutes for acquisition of the dose rate for each organ, and the average clinical procedure time was multiplied by each organ dose rate for acquisition of individual organ doses. The effective dose was computed by summing the product of each organ dose and the corresponding tissue weighting factor from International Commission on Radiologic Protection publication 60. The effective dose was computed as 0.93 mSv for an average lumbar epidural steroid injection procedure (fluoroscopic time, 40.7 seconds). The corresponding kerma area product was 2.80 Gy.cm(2). The dose conversion coefficient was derived as 0.33 mSv/(Gy.cm(2)). The effective dose for lumbar epidural steroid injection can be easily estimated by multiplying the derived dose conversion coefficient by the console-displayed kerma area product.