Low doses of radiation: When hormesis and abscopal effect meet ...

Nuclear medicine, on its diagnostic side, provides real medical services allowed by scintigraphic examinations, clinically useful and changing patient management. However, this results in the global and heterogenous irradiation of patients, delivering prolonged and continuous exposure at low (or very low) dose rates which inevitably raises the question of possible stochastic effects ... On the other hand, on its therapeutic side, nuclear medicine, using much higher activities, claims to treat or cure some cancers. This apparent contradiction can be solved by recalling some important concepts, poorly known as recent but very likely to usefully illuminate the debate on the effects of low and very low doses, and especially to introduce some consistency. The effect of ionizing radiation, at low doses, is ambivalent and must be interpreted through a dynamic equilibrium between two phenomena acting in opposite directions: on one hand, the contribution of radiations contributes to potentially deleterious lesions; on the other hand the stimulation by these same radiations of mechanisms of defense, especially immunological, against the induction of tumors. This gives them a true systemic action, which corresponds, in the case of proven cancer, by the so called "abscopal effect", whose understanding is similar to that of the phenomenon of hormesis, in favor of a reduction in the risk of cancer at (very) low doses. These concepts undermine the RLSS (linear relationship without threshold), and open new fields of research to better understand and master the modalities of IRV (Internalized Radiotherapy Vectorized). The effects of low doses can only be considered in a dynamic and integrated way. Radiation-induced carcinogenesis is in fact a threshold effect, which cannot be extrapolated linearly below this threshold. (C) 2019 Elsevier Masson SAS. All rights reserved.