The Effect of Stepping Back From the X-Ray Table on Operator Radiation Exposure

Abstract

Background: Nearly all radiation safety courses teach that scatter radiation around the x-ray table falls with the inverse of the distance from the imaging site. Humans, however, are complex x-ray reflectors and the application of the inverse square law to clinical imaging is only assumed. Methods: We measured scatter radiation at two positions where staff commonly stand around the x-ray table. Using an anthropomorphic human phantom, human and pig cadavers, and a glass sphere, we measured scatter radiation levels in each position, and then 2- and 3-fold the distance from the imaging site. We compared the measured scatter radiation to that predicted by the common inverse square law and a more detailed geometric inverse square law. Results: In all but the glass sphere, scatter radiation was much higher below the table (68–74% of all scatter radiation, depending on model and position) than above the table (26–32% of scatter radiation, p < 0.01). Scatter radiation fell with increasing distance from the table, but above the table both inverse square laws significantly over-estimated the benefit of stepping back (19–93% overestimation by geometric inverse square law at 2-fold distance, 14–46% at 3-fold). In addition, a pelvis in the phantom appeared to cause significant scatter radiation field anomalies at the angiographer position. Conclusion: Stepping back from the table does not reduce scatter radiation levels as much as the inverse square law predicts. The geometric inverse square law best predicts the reduction in scatter radiation below the table, but above the table it too overestimates the benefit of stepping back. The irregularity of the scatter radiation field should be taken into account by scatter radiation shielding systems.

Scatter Radiation Distribution to Radiographers, Nearby Patients and Caretakers during Portable and Pediatric Radiography Examinations

“…It has been long assumed that the scatter radiation will decrease with increasing distance by inverse square law. However, the irregularity of scatter radiation may reduce the effects of radiation dose reduction by increasing distance as pointed out by a recent study [6]. For the use of shielding, it has been commonly found that physical shielding has not been used in ward settings due to weight and mobility concerns [2].…”