PMC

T1-weighted gadolinium-enhanced MRIs of the brain. Delineated in red (A) is a lesion that developed adverse radiation effects after stereotactic radiotherapy and (B) a lesion that did not develop adverse radiation effects after stereotactic radiotherapy.

Conceptual model of UV‐B radiation effects on the whole plant.

Radiation effects on trabecular bone microarchitecture at days 3 and days 21 as measured by μCT. Image courtesy from Lima et al. [].

A diagram schematizing the original definition, current situation and our proposal for radiation effect classification and associated radiation protection (RP) endpoints. Orange- and green-colored solid lines indicate radiation effects of which risk is managed in terms of mortality and incidence, respectively. Yellow- and blue-colored solid areas represent radiation effect categories. The yellow-colored dotted line shows radiation effects categorized in tissue reactions but with a linear-non-threshold (LNT)-like dose response, whereas the blue-colored dotted line shows radiation effects categorized in stochastic effects but with a threshold-like dose response. A purple-colored dotted line further emphasizes radiation effects that obscure the boundary between stochastic effects and tissue reactions. Radiation effects were originally classified into stochastic effects and non-stochastic or deterministic effects (presently called tissue reactions). Stochastic effects comprise fatal cancer, non-fatal cancer (e.g. thyroid cancer and non-melanoma skin cancer) and fatal hereditary effects with an LNT dose–response model, whilst a threshold-like dose–response relationship has been known for several cancers such as skin cancer and bone cancer. Non-stochastic or deterministic effects include radiation effects with a threshold-type dose–response model (e.g. vision-impairing cataracts and cosmetically unacceptable non-cancer skin changes). For RP purposes, mortality and incidence were endpoints employed to manage the risk of stochastic effects and non-stochastic or deterministic effects, respectively, whereas an ‘emergency dose level’ for the thyroid was assigned based on its cancer incidence. At present, these have not been changed basically. However, a tissue reaction category now includes life-threatening circulatory disease, though its dose limit has not been set. Moreover, for cataracts and circulatory disease, epidemiological evidence now suggests an LNT dose response, and the RP system assumes no dose-rate effect, making the boundary between stochastic effects and tissue reactions fuzzy. Such a situation may be improved if radiation effects are classified into life-threatening disease and non-life-threatening disease, for which the risk management endpoints are mortality and incidence, respectively. Taken together, the necessity to limit heritable effects should also be reconsidered because human evidence has thus far shown no detectable transgenerational effects. This approach may be useful for future discussion.