Recommendations of the National Council on Radiation Protection and Measurements: Sources and Magnitude of Occupational and Public Exposures from Nuclear Medicine Procedures

Abstract

Previous reports by NCRP have covered various aspects of patient exposure from, and practical advice on, the use of radioisotopes in medical laboratories. This report deals with the exposure of four main groups: staff in nuclear medicine laboratories, other hospital staff, patients and other members of the public. The total number of nuclear medicine procedures in the United States at the start of the decade was about 100 million, some 90% of these were radioimmunoassay investigations, and the remainder were in vivo administrations of radioactive materials. The number of in vivo nuclear medicine procedures increased by about 16% from 6.4 million to 7.4 million from 1980 to 1990. This was less than the projected 8% per year increase expected over that period because of the virtual disappearance of some techniques, such as the use of for brain scintigraphy and sulphur colloid liver imaging. Computed tomography and magnetic resonance imaging have largely replaced those techniques. Some other techniques such as positron emission tomography for mapping certain functions of the brain show an increasing trend. Radionuclides used for organ imaging, for example , emit penetrating gamma radiation and give rise to occupational exposure of nuclear medicine staff and other persons in the vicinity of patients undergoing diagnosis or treatment. The dose to a patient from a nuclear medicine diagnostic procedure is typically in the range 0.1 mSv to 10 mSv. The dose rate at 1 m from a typical diagnostic patient is about , after administration of 0.74 GBq of . Therapeutic administrations, for example 3.7 GBq of , will give rise to a dose rate of about at 1 m from the patient, who will normally need to be segregated to reduce the exposure of other persons in the vicinity. Samples, such as blood, taken from a patient also represent a source of staff exposure and the report discusses the requirements for shielding these samples. Work involving the preparation and assay of radiopharmaceuticals tends to be associated with the highest occupational exposures in this field, and can give rise to annual doses up to about 5 mSv. However, doses to hands and fingers can range up to the annual limit of 500 mSv and various shielding devices can be used to reduce extremity doses. However, the majority of workers in nuclear medicine departments who are not directly handling radiopharmaceuticals receive very low exposures, typically well below 1 mSv. Members of the patient's family may sometimes be in close proximity to the patient after the administration of radiopharmaceuticals. Studies cited in the report suggest doses up to about per procedure might be received by these individuals. To estimate the radiological impact of these procedures on the general public it is assumed that a dose of is received by a member of the public from each in vivo procedure and the annual per caput dose to the US population, not including patient dose, is evaluated as . The risks represented by the occupational doses received from this work are also considered in this report. Other topics covered are dosage calibration, contamination control and radioactive waste disposal. There is also a section containing specific advice for nursing staff. It therefore covers virtually the whole subject, albeit briefly - the main report is some 40 pages long. It contains much up-to-date information and advice and is a welcome addition to the literature.