Entrance skin dose
The entrance skin dose 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) 1. Entrance skin dose is often a benchmark measurement used to assist in quality control and optimisation in radiography departments.
They are used in plain radiography to set diagnostic reference levels, a reference level that establishes a benchmark for the optimisation in using medical radiation, ensuring departments adhere to the principles of radiation protection 2.
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 3:
- 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 3.
- 1. ICRP, 1996. Radiological Protection and Safety in Medicine. ICRP Publication 73. Ann. ICRP 26 (2).
- 2. Australian Radiation Protection and Nuclear Safety Agency. National Diagnostic Reference Level Fact Sheet. Miranda: Australian Government, 2017.
- 3. Basic Physics of Digital Radiography/The Patient - Wikibooks, open books for an open world". En.wikibooks.org, 2017. [Link].