PHYSICAL REVIEW E 99, 022139 (2019) Radiation adaptive response and cancer: From the statistical physics point of view Krzysztof W. Fornalski * National Centre for Nuclear Research (NCBJ), ulica A. Soltana 7, 05-400 Otwock- ´ Swierk, Poland and Ex-Polon Laboratory, ulica Podle´ sna 81a, 05-552 Lazy, Poland (Received 3 October 2018; revised manuscript received 2 February 2019; published 26 February 2019) Elements of statistical physics formalism were applied to mutagenic and carcinogenic processes associated with cellular DNA; these are lesion (damage) creation, mutation creation, and cellular neoplastic (cancer) transformation. The probabilities of all state changes were strictly related to potential barrier heights between energetic states of DNA molecules. Barriers can be modified when radiation adaptive response mechanisms are applied, which are associated with a radiobiological quantity called radiosensitivity. It was discussed that radiosensitivity is determined by the cell’s response to radiation resulting in three potential dose-response scenarios: linear, threshold, or hormetic. The type of dose-response is of critical importance in the development of radiation protection standards and individual radiation risk assessment. It is shown that the different scenarios describe different limits of the same underlying phenomena and the cell can respond in a linear, threshold, or hormetic way regarding its radiosensitivity. Finally, the dissipative adaptation mechanism is discussed in the context of proliferating cancer cells. DOI: 10.1103/PhysRevE.99.022139 I. INTRODUCTION The radiation adaptive response is a biophysical phe- nomenon which may appear in organisms irradiated by low doses of ionizing radiation. This effect stimulates natural mechanisms responsible for antioxidants, apoptosis, immune system, and DNA repair processes, reducing the risk of neo- plastic transformation of irradiated cell(s) [1–4]. There are many ways in which the adaptive response can be presented. The easiest way for experimenters is when the adaptive response is associated with a small priming radiation dose that reduces a significant portion of the detrimental effects of a higher challenging dose; this is called the priming dose effect [5]. The radiation adaptive response may be a special case among the wider adaptation processes of every living organism [6]. The concept that the general dose-response relationship for low doses of ionizing radiation is potentially nonlinear has a crucial importance for existing radiation protection standards. In fact, one can observe many scientific discussions worldwide as to which model of radiation risk curve should be the appropriate one [4,7–9]: (a) linear dependence (so-called linear no-threshold model, LNT, which assumes that all radiation implies some risk of cancer induction), (b) threshold dependence (which assumes that radiation is dangerous only above some exact value), (c) hormetic dependence (which assumes that low doses of ionizing radiation are beneficial for an organism’s health). The discussion of which model is better has been ongoing for years. However, the important point is that each model claims to have experimental data which support it; therefore, it * krzysztof.fornalski@gmail.com is hard to clearly state which one is the only possible solution [10]. Each of the three dose-response models has its own sup- porters, experimental data, and many mathematical or bio- physical concepts to explain it. For example, one can simulate an irradiated cell’s behavior using a stochastic or analytic approach [11–14]. Also, a physical formalism from pure thermodynamics can be applied to predict organism response to irradiation [15]. However, the biggest challenge would be to create a more general model which can join all three completely different relationships into a single one. A few years ago, England proposed a concept of life creation associated with “dissipative adaptation in driven self-assembly” [6,16,17]. There is a fundamental biophysical difference between living organisms and, for example, a group of carbon atoms. Living organisms deal much better with obtaining energy from the environment and releasing it as heat (dissipation). In England’s theory, when a group of atoms is exposed to an external energy source, such as from the sun, ionizing radiation, or chemical reactions, and surrounded by a thermal bath (e.g., atmosphere or ocean), it will gradually be transformed to spread out more and more energy. Un- der certain conditions, matter will inevitably acquire some fundamental physical properties that are identical with life [18]. The essence of England’s theory is the generalization of the second law of thermodynamics for particle systems with specific features. These systems are strongly dependent on an external energy source, such as from an electromagnetic wave, and release the heat to the surrounding thermal bath. Each living organism can be treated as such a system—and these systems change over time [6,16,17]. The overall system’s behavior (namely, self-replication or aging) becomes more and more irreversible [16,17]. It can then be shown that the course of evolution is more likely, which assumes obtaining more energy from the environment 2470-0045/2019/99(2)/022139(8) 022139-1 ©2019 American Physical Society