Chapter

Therapeutic Nuclear Medicine

Part of the series Medical Radiology pp 789-805

Date:

Hormesis by Low Dose Radiation Effects: Low-Dose Cancer Risk Modeling Must Recognize Up-Regulation of Protection

  • Ludwig E. FeinendegenAffiliated withHeinrich-Heine-UniversityBrookhaven National Laboratory Email author 
  • , Myron PollycoveAffiliated withSchool of Medicine, University of California San Francisco
  • , Ronald D. NeumannAffiliated withRadiology and Imaging Sciences, Clinical Center, The National Institutes of Health

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Abstract

Ionizing radiation primarily perturbs the basic molecular level proportional to dose, with potential damage propagation to higher levels: cells, tissues, organs, and whole body. There are three types of defenses against damage propagation. These operate deterministically and below a certain impact threshold there is no propagation. Physical static defenses precede metabolic-dynamic defenses acting immediately: scavenging of toxins;—molecular repair, especially of DNA;—removal of damaged cells either by apoptosis, necrosis, phagocytosis, cell differentiation-senescence, or by immune responses,—followed by replacement of lost elements. Another metabolic-dynamic defense arises delayed by up-regulating immediately operating defense mechanisms. Some of these adaptive protections may last beyond a year and all create temporary protection against renewed potentially toxic impacts also from nonradiogenic endogenous sources. Adaptive protections have a maximum after single tissue absorbed doses around 100–200 mSv and disappear with higher doses. Low dose-rates initiate maximum protection likely at lower cell doses delivered repetitively at certain time intervals. Adaptive protection preventing only about 2–3 % of endogenous lifetime cancer risk would fully balance a calculated-induced cancer risk at about 100 mSv, in agreement with epidemiological data and concordant with an hormetic effect. Low-dose-risk modeling must recognize up-regulation of protection.

Keywords

Low-dose cancer risk Adaptive protections Hormesis