Needs for radioactivity standards and measurements in the life sciences.

For almost 100 years, radioactivity has been one of the major tools in medicine. Therapeutic applications that began with 226Ra and 222Rn implants have rapidly grown to include about 20 radionuclides with radiations specifically chosen to treat at different depths in tissue--ranging from a few millimeters for intravascular therapy to a few centimeters in the case of large solid tumors. Systemic treatments with radiopharmaceuticals have grown from the traditional 131I to more than ten candidate nuclides which are to be labeled to tumor-specific radiopharmaceuticals. Diagnostic radiopharmaceuticals are used in over 13 million procedures in the United States annually. About 40 nuclides are under investigation for these applications including single photon emitters for SPECT (single photon emission computed tomography) and positron emitters for PET (positron emission tomography). In addition to the mainstays of therapeutic and diagnostic radiology, radionuclides are widely used for in vitro tracers in the life sciences and represent one of the main tools in the field of molecular biology.