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X-Ray Section: X-Ray Guidance: Measured ESE Data
Patient exposure from diagnostic x-rays is often reported as the Entrance Skin Exposure (ESE). ESE is the amount of radiation that enters the patient's body closest to the primary source of x-ray radiation. While not directly related to risk, the values can be used to compare patient exposures at different facilities for the same procedures.
Inspectors measure ESE in units of milliroentgen. They calculate the milliroentgen per milliampere-second (mR/mAs) factor for the peak tube potential (kVp) values used and provide this information to the facility. The mR/mAs factor can then be used to estimate ESE's for various procedures, which can then be compared with reference data to evaluate machine and operator performance. Changes in exposure due to changes in mAs and kVp can be estimated using the mR/mAs factor.
ESE studies are being performed by both the Food and Drug Administration's National Evaluation of X-ray Trends (NEXT) program and the Utah Division of Radiation Control's ESE program. An important conclusion from both studies is that a wide range of patient exposure occurs in diagnostic radiology. For example, the ESE for an x-ray of a hand is only a few milliroentgens. However, the ESE can be several thousand milliroentgens in fluoroscopy. This wide range of exposures is expected and hardly surprising. What is surprising is that even for the same routine procedure and for the same average size adult, exposures vary substantially between facilities.
X-ray's of an average adults abdomen can result in an ESE ranging from 21 mR to 2575 mR, with an average value of 366 mR! Some of the variation can be attributed to a difference in the clinical criteria of what is considered an acceptable film image by the medical professional reviewing the x-ray film. These criteria will affect the decision on what film imaging system is used and what technique factors are employed for a particular procedure. However, another contributing factor in the observed variation in patient exposure can be attributed to the use of suboptimal imaging equipment, poor choice of technique factors, and/or incorrect film processing procedures.
Knowledge of ESE's is important because of the growing acceptance by the public as well as the medical community of the need to be aware of the patient exposures used during various diagnostic x-ray procedures. In part, this acceptance has been inspired by an increasing number of patient inquires concerning exposures. It has also been motivated by the radiology community's desire to optimize the diagnostic use of radiation while minimizing patient exposures.
The Division's ESE program acts as a resource for patient exposure. The program's objective is to measure and provide healing arts facilities with patient exposure information. This includes Entrance Skin Exposure, ESE values for common radiographic procedures and comparative exposure data. This information is to assist facilities in deciding whether patient exposures are acceptable. In those situations where a facility feels the exposures are too high, the Division can offer practical solutions to reduce patient exposure.
If you have additional questions regarding X-rays, please contact a member of the X-ray staff at 801-536-4250 or you may contact us through e-mail.
