The effect of stepping back from the x-ray table on operator radiation exposure

Robert F. Wilson, John P. Gainor, Blair Allen

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)522-530
Number of pages9
JournalHealth Physics
Issue number5
StatePublished - Nov 1 2021

Bibliographical note

Funding Information:
Robert Wilson is a co-founder and CEO of Egg Medical and the Chief Scientific Officer of Acist Medical. Inc. Mr. Gainor and Mr. Allen are employees of Egg Medical, Inc. Sources of Funding: Egg Medical supplied the radiation meter and the anthropomorphic phantom.

Publisher Copyright:
© 2021 LWW. All right reserved.


  • Diagnostic radiology
  • Radiation dose
  • Radiation protection
  • X-ray imaging

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't


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