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RAD & REM X-Ray Radiation Safety Levels

Since the X-ray was discovered in 1895, its exposure has been known to to be detrimental to the health of patients and X-ray practitioners. In 1964 the National Council on Radiation Protection and Measurements (NCRP) was chartered by the U.S. Congress.The NCRP states recommendations for maximum permissible radiation exposure for patients and X-ray operators. The fundamental unit of measurement of X-ray energy is the roentgen (R). A roentgen, RAD and REM are all the same quantity of radiation.

  1. RAD -- Patient Exposure

    • RAD stands for roentgen absorbed dose. It's equivalent to an exposure of 1 R to a patient or someone who does not work with radiation. The non-occupational, whole-body dose limit or maximum permissible dose (MPD) is 500 MRAD (milli-RADs) per year. This is equivalent to 50 chest X-rays per year. Radiation doses are not typically monitored in the general public unless the patient is undergoing radiation therapy.

    REM -- Occupational Exposure

    • REM stands for roentgen equivalent man. One REM is equivalent to an occupational exposure of 1 R. The occupational MPD limit is 5000 MRADs (5 RADs) per year. This applies to the head, neck, trunk, lens of the eye, blood-forming organs and gonads. Other body parts have different MPDs. For example, the MPD for the hands is 30 REM per year. Some radiographers and nuclear medicine technologists receive higher extremity doses and must wear radiation monitors on their hands.

    Monitoring Occupational Exposure

    • By federal law, radiation workers must monitor their occupation-related radiation exposure. Radiation workers wear monitors, usually in the form of badges or rings. The monitor contains a lithium fluoride chip that absorbs X-ray energy and stores it in its crystal lattice. The chip is later processed by heating. When the lithium fluoride chip is heated the X-ray energy is converted and given off as light. The measured light intensity is proportional to the radiation dose received by the chip.

    Radiosensitivity of Tissues

    • Certain anatomical tissues are more radiosensitive (susceptible to radiation damage) than others. These include the lymphoid organs, bone marrow, blood, testes, ovaries and intestines. In general, the newest and most rapidly reproducing tissues are the most radiosensitive. Fetuses are especially vulnerable.

    Fetal Dose Limits

    • Pregnant workers should be monitored closely for radiation exposure.

      Because the developing fetus is especially sensitive to radiation, pregnant radiation workers must be closely monitored to prevent radiation injury their unborn child. For a pregnant woman working in radiological areas, the dose limit for the embryo/fetus (during entire gestation period) is 0.500 REM and should not exceed 50 milli-REMs per month.

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