不論是作爲診斷用途或治療用途，研究放射性藥物在微觀量七分佈情形的迫切及重要原因，乃是能藉此研究預測在遺傳物質上放射性藥物發射放射性所引起的效應及影響。一般在放射性藥物的領域之中，診斷和劑量學皆以放射性示蹤劑在體內數公釐的巨觀分佈爲基礎。近年來對於在細胞和次細胞層次的微觀分佈的探討研究使放射性藥物在生化機制上的瞭解獲得比純理論更實用的數值。在本文中將說明微劑量學之範疇所代表的意義，並介紹微劑量學的發展形成及理論基礎，最後將探討微劑量學在放射醫學上的關連及其發展應用。

The understanding of localization mechanisms and microdosimetry of diagostic and therapeutic radiopharmaceuticals depends on knowledge of their biodistribution at the microscopic level (cellular and subcellular) in the target tissues. Both diagnosis and dosimetry are usually based on the macroscopic distribution of radiotracers in the body with a resolution of several millimeters. However, it is becoming increasingly recognized that knowledge of the distribution at microscopic level can acquire practical value beyond the obvious "academic" desirability of greater biochemical understanding. Here we will describe the difference between macrodosimetry and microdosimetry, the theory and application of microdosimetry. This paper discusses the microdosimetric quantities and dose distributions, and also the relationships and applications of microdosimetry for radionuclides.