If you reveal your secrets to the wind, you should not blame the wind for revealing them to the trees. —From The Prophet by Kahlil Gibran This was a very satisfying book to write, but also perhaps a very dangerous one. After 15 years of building a base of knowledge in radiopharmaceutical dosimetry (under the expert guidance of Evelyn Watson at the Oak Ridge Dosimetry Center), 8 years of teaching radiation protection and dosimetry at the university level (in northeastern Brazil and at Vanderbilt University in the United States), and Photo used with permission. Copyright © OregonVacationBeaches.com. Also see Memorable-Beach-Vacations.com. v vi Preface authoring a number of papers and book chapters on the subject, it was rewarding to write down in a single, organized text nearly all that I have learned on this topic. My deepest desire is that this text will be found useful by members of the nuclear medicine and radiation protection community in formalizing and facilitating such calculations. After learning a technique for performing dose calculations that must be done often, I have often found ways to automate such work in software tools and to make such tools available to others in order to help them shortcut their efforts. One of the greatest rewards I have received in my work has been to see a few of the tools and ideas that I have developed become useful to others in their routine work.