Entrance skin dose

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The entrance skin dose (or entrance surface dose), abbreviated as ESD, is the measure of the radiation dose that is absorbed (mGy) by the skin as it reaches the patient. Entrance skin dose is a directly measurable quantity, often, measured using thermoluminescent dosimeters (TLD) . Entrance skin dose is often a benchmark measurement used to assist in quality control and optimization in radiography departments. However, it is a poor indication of radiation risk as it does not account for tissue sensitivity, penetration and area of the x-ray beam.

They are used in plain radiography to set diagnostic reference levels, a reference level that establishes a benchmark for the optimization in using medical radiation, ensuring departments adhere to the principles of radiation protection .

At the time of writing this article (April, 2017) the following entrance skin dose recommendations for an adult of average size (70-80 kg) in plain radiography exist set by the Australian Radiation Protection and Nuclear Safety Agency :

  • skull AP/PA:  3 mGy
  • skull lateral: 1.5 mGy
  • chest PA: 0.2 mGy
  • chest lateral: 1.0 mGy
  • thoracic spine AP: 3.5 mGy
  • thoracic spine lateral: 10 mGy
  • lumbar spine AP: 6 mGy
  • lumbar spine lateral: 14 mGy 
  • lumbar spine spot: 26 mGy
  • abdomen AP: 6 mGy
  • pelvis AP: 4 mGy

Factors that contribute to an increase in entrance skin dose include body habitus (obese patients can have a dose increase reaching factors of 80) and poor radiographic positioning .