The quest for the laws governing radiations and the search for beneficial innovations

The last few years of the 19th Century saw the initial discoveries of ionizing radiation. These seminal discoveries were followed by an era of intensive studies of the physics related to radiation and clinical applications. The quantum theory revolutionized the ideas about nuclear structure and had a major impact on the physics of radiation. The discoveries of artificial radioactivity and of the neutron and the associated nuclear research have led to the availability of a variety of labeled compounds important to the study of human metabolism. Radioimmunoassay is an example, while other labeled compounds have therapeutic significance. New concepts in the acceleration of electrons and positive ions have contributed to the ability to concentrate radiation energy. New concepts in physics have led to the development of significant and versatile forms of diagnostic imaging. An example is computed tomography. Magnetic resonance is another example of an important physical concept which, decades after its discovery, made possible important applications in imaging and spectroscopy. Unlike ionizing radiation, the less energetic radiofrequency photons can convey information about molecular bonds but do not have sufficient energy to break them. Photon and positron emission scanning and tomography provide external images of internal concentrations of radionuclides, permitting the noninvasive determination of function. Dosimetry is fundamentally important to the diagnostic and therapeutic uses of radiation at both microscopic and macroscopic levels. A variety of radiation measuring instruments have been designed and studied for different purposes, including those based on radiation chemical response. Mammography is just one of the diagnostic applications where dosimetry, detector sensitivity characteristics, the radiation energy spectrum and image resolution are all vital parameters. In radiation treatment, physical and mathematical developments and quantitative radiation biology have increasingly led to optimum conformal radiation treatment, with dosimetry as a guiding parameter.