PNNL

Abstract

The current applications for the in vivo measurement of radioactive material can be divided into three broad categories: 1) occupational exposure monitoring, 2) monitoring of the public, and 3) medical monitoring. The focus of this chapter is on occupational exposure monitoring that is part of an internal dosimetry program for monitoring workers for intakes and assessing the dose consequences of an intake. In the 1920's when electroscopes were first used to measure radium in the body of dial painters issues affecting the measurement accuracy were identified related to external contamination interferences, properly measuring the instrument background, need for measurement QC, microphonic interferences, shielding and others. The sophistication of the radiation detection instrumentation has evolved to the point where most systems today employ one or more detectors primarily either sodium iodide or germanium. Many different styles of detectors and cryostat designs are used at different facilties. However, the same issues identified in the 1920's are still issues today. The in vivo measurement systems are calibrated with anthropometric phantoms that simulate the body or parts of the body. Whole body phantoms, torso phantoms, lung phantoms, thyroid phantoms and skeletal phantoms are just some of the different types used.The systems are typically shielded with low background materials such as pre-World War II steel from battelships. Interferences can come from naturally occurring radioactive material, medically administered radiopharmaceuticals, equipment instability, non-ionizing elecromagnetic radiation and other sources. These contribute to the uncertainties in measurement resutls that can range from 10% to 1000% or more depending on the measurmeent system, the energy of the radiation associated with the radionuclide to be meausred, the accuracy of the phantom versus the person espacially how well the distributions of activity match.