Authorized User and Radioisotope Safety Issues

Authorized User

Nuclear medicine activities in any department or outpatient imaging center take place under the supervision and authorization of an authorized user, also referred to as an AU. An AU is a physician (medical or osteopathic), dentist, or podiatrist who is licensed to practice and who meets specific requirements and is identified as an AU on the institution's license or permit. All radiopharmaceuticals dispensed or administered must be pursuant to an order (e.g., prescription) of an AU. For most diagnostic radiopharmaceuticals, this does not need to be done for each patient individually but can be accomplished with standing orders. However, for radiopharmaceuticals used for therapy, and in some other circumstances detailed later in this chapter, a written directive, which may only be issued by an AU, is required for each treatment. Other physicians and technologists may work with byproduct material under the supervision of an AU.

Institutions with a broad-scope license may have AUs designated by the Radiation Safety Committee, but they are not listed on the license. With a limited-scope license, which constitutes the majority of licenses, the AU must be listed on the license and there must be at least one AU for every classification of clinical use designated on the license. Training requirements for an AU vary, depending on the type of procedure. The training requirements are covered in several following sections. Some items with which an AU should be very familiar are shown in Box 13.1 .

Radiation Safety Officer

A radiation safety officer (RSO) is typically a health physicist or medical physicist who must meet substantial additional training and experience requirements. Every radioactive materials license must list one permanent RSO. A licensee may appoint and name on the license a qualified individual with expertise in certain areas to serve as an Associate RSO (ARSO). This individual will be required to complete the same training and experience requirements as the named RSO for the individual’s assigned sections of the radiation safety program. The ARSOs will have oversight duties for the radiation safety operations of their assigned sections, while reporting to the named RSO. The regulations allow a licensee to name only one RSO on a license. The RSO will continue to be responsible for the day-to-day oversight of the entire radiation safety program. An RSO is responsible for implementing the radiation safety program and ensures that activities are being performed in accordance with approved procedures and regulatory requirements. The RSO must meet the training requirements outlined in the Federal Regulations, 10 CFR, Part 35.50. Recently, NRC rules have been modified so that Authorized Users, Authorized Medical Physicists, and Authorized Nuclear Pharmacists who (1) have met the requirements to serve as the RSO or ASRO and (2) are listed as such on their institutional license may be listed on any other medical use license to serve as an RSO or ASRO. Additionally, these ARSOs and RSOs may serve as preceptors for an individual seeking to be named as the RSO.

Duties of the RSO include investigating overexposures, accidents, and other mishaps and collecting or establishing written policies and procedures relative to purchasing/ordering, receipt and opening, storage, inventory, use, and disposal of byproduct material. The RSO is also responsible for performing checks of survey instruments and other safety equipment, training personnel, performing radiation surveys, retaining copies of reports and policies, briefing management once each year, and establishing investigational levels of personnel exposure (which when exceeded, initiates an investigation by the RSO) and taking emergency action if control of radioactive material is lost. For up to 60 days each year, a licensee may permit one or more AUs or individuals qualified to be an RSO to function as an RSO.

Other Authorized Personnel

An authorized medical physicist is an individual who is predominantly involved with high-energy external beam radiotherapy, brachytherapy, and stereotactic radiosurgery and who has little involvement with most diagnostic nuclear medicine operations. Specific training requirements can be found in 10 CFR, Part 35.51. An authorized nuclear pharmacist is identified as such on the facility license or permit and must meet requirements specified in 10 CFR, Part 35.55. These individuals are usually employed in commercial or large institutional radiopharmacies.

Occupational

Occupational dose is that received in the course of employment in which the individual's assigned duties involve exposure to radiation or radioactive material from licensed and unlicensed sources of radiation whether in the possession of the licensee or other person. Occupational dose does not include doses from (1) natural background radiation, (2) medical exposures of the individual, (3) exposure to persons who have been administered radioactive material and released, (4) voluntary participation in medical research, or (5) as a member of the public.

A licensee must demonstrate that unmonitored individuals are not likely to receive in 1 year a radiation dose in excess of 10% of the allowable occupational limits or they must monitor external and/or internal occupational radiation exposure to such individuals. Practically speaking, this 10% rule governs who should wear a film badge (or other monitoring device) in a nuclear medicine facility.

Public

Public dose is that received by a member of the public from exposure to radiation or to radioactive material released by a licensee. Public dose does not include (1) occupational exposure, (2) medical exposures the individual has received, (3) exposure to natural background radiation, (4) any medical exposure from another person who has received radioactive material and been released, or (5) voluntary participation in biomedical research.

Embryo/Fetus

An embryo/fetus is subject to a dose equivalent limit of less than 0.5 rem (5 mSv) during the entire pregnancy from occupational exposure of a woman who has declared her pregnancy. This is true even though the mother may be subject to higher occupational exposure limits in her employment. If the dose equivalent to the fetus is found to have exceeded 0.5 rem (5 mSv) or is within 0.05 rem (0.5 mSv) of exceeding this dose by the time the woman declares the pregnancy to the licensee, the licensee is in compliance as long as the additional dose equivalent to the embryo/fetus does not exceed 0.05 rem (0.5 mSv) during the remainder of the pregnancy. It should be noted that there is no fetal dose limit if the pregnancy is not declared to the employer.

Breastfeeding

Breastfeeding cessation is not regulated, but there are NRC guidelines. Cessation is not needed for fluorine-18-fluorodeoxyglucose ( ¹⁸ F-FDG), and cessation times for technetium radiopharmaceuticals range from 0 to 24 hours. Breastfeeding is usually discontinued for a week or more for thallium-201, gallium-67, and indium-111 pharmaceuticals. Breastfeeding is contraindicated for several months after radioiodine therapy (see Appendix G ).

Family and Caregivers

In 1997, the NRC amended its regulations for the release of patients receiving treatment with radioactive materials from an activity-based limit to a dose-based limit. The regulation was based on the maximally exposed individual (including family or caregivers) not being likely to exceed an effective dose equivalent of 0.5 rem (5 mSv) from this single radioisotope treatment (see Appendix H.2 ). Compliance with the dose limit is demonstrated by (1) using a default table for activity or dose rate or (2) performing a patient-specific dose calculation. If the total effective dose equivalent to any other individual is likely to exceed 1 mSv (0.1 rem), written radiation safety guidance (instructions) to reduce this dose through ALARA practices is required to be given to the patient. There is no specific guidance with regard to radiation exposure of pregnant women through contact with the treated patient, but it does indicate that written instructions must be provided if a nursing child of the patient is likely to exceed an effective dose of 100 mrem (1 mSv). These instructions must include (1) guidance on interruption or discontinuation of breastfeeding and (2) the potential consequences of not following this guidance.

Dose Calibrators and Survey Instruments

If radiopharmaceuticals and patient dosages are prepared on-site, the licensee must possess and use instrumentation to measure the activity of unsealed byproduct material before it is administered to each patient. The instrument (dose calibrator) must also be calibrated according to nationally recognized standards or the manufacturer's recommendations. Survey instruments must also be calibrated before first use, annually, and after repair. All scales with readings up to 1000 mrem (10 mSv) must be checked for accuracy by obtaining two separate readings on each scale, and the indicated exposure must be within 20% of the calculated exposure. Dates of calibration must be indicated on the instrument. Records of the information, including serial number of instruments, names of those performing the calibration, and dates must be kept for 3 years.

Determination and Records of Dosages

The licensee needs to determine and record the activity of each dosage before medical use. For patient unit doses supplied by a commercial radiopharmacy, there must be direct measurement or a decay correction based on the activity determined by the licensed preparer. For other than unit doses (usually multidose vials), determination of activity for each individual patient dosage must be made by direct measurement (dose calibrator), a combination of measurement and mathematical calculations, or combinations of volumetric measurements and mathematical calculations. Unless specified by the AU, a licensee may not use any dosage if it falls outside of the prescribed dosage range or differs from the prescribed dosage by more than 20%. Records of dosage determination must be retained for a period of 3 years and must contain the name of the radiopharmaceutical, patient's or subject's name or identification number, the prescribed dosage or a notation that the total activity is less than 30 µCi (1.1 MBq), date and time of administration of the dosage, and the name of the individual who determined the dosage.

Calibration, Transmission, and Reference Sources

In addition to patient imaging and treatment, radioisotope sources are used for instrument calibration and quality control purposes as well as for transmission images. Any person authorized for medical uses of byproduct material may receive, possess, and use byproduct material for check, calibration, transmission, and reference use. This includes sealed sources not exceeding 30 mCi (1.11 GBq) provided or redistributed in original packing by a licensed manufacturer. Possession also includes byproduct material with a half-life of not longer than 120 days in individual amounts not to exceed 15 mCi (0.56 GBq) or byproduct material with a half-life of longer than 120 days not to exceed the smaller of 200 µCi (7.4 MBq) or 1000 times the quantity in Appendix B of Part 30 of 10 CFR. One can also possess technetium-99m ( ^99m Tc) for these purposes in amounts as needed.