26 Dosimetry in Pediatric Nuclear Medicine

The science of internal dosimetry is a specialty within the general field ofhealth physics. A working definition ofhealth physics might be "the protection of people and their environment from the harmful effects of radiation while allowing its beneficial applications." With any application involving the use of ionizing radiation, the risks of its use must be balanced against its benefits. With medical uses of radiation, the benefits are immediately obvious and are directly received by the person exposed to the risk. This makes the balancing process considerably easier than, for example, the use of nudear power, where a small number of people incur a risk so a broad region can receive a benefit. This balance, however, cannot be evaluated without some quan­ tification of the risks. Internal dosimetry calcula­ tions provide estimates of the amount of radiation that is absorbed by different organs or organ sys­ tems. The assignment of a risk to a given radiation dose estimate is not a dear-cut procedure, but with­ out the absorbed dose estimate it cannot be at­ tempted. This chapter outlines the basic concepts inherent in current dose calculations, describes the calcula­ tional framework, and provides dose estimates for a number of radiopharmaceuticals in use in pediatric nudear medicine today (Table 26.1). A more exten­ sive discussion of these concepts, with demonstra­ tion by several practical examples, may be found in the MIRD Primer.49