Neutron relative biological effectiveness in Hiroshima and Nagasaki atomic bomb survivors: a critical review

Abstract

The calculated risk of cancer in humans due to radiation exposure is based primarily on long-term follow-up studies, e.g. the life-span study (LSS) on atomic bomb (A-bomb) survivors in Hiroshima and Nagasaki. Since A-bomb radiation consists of a mixture of γ-rays and neutrons, it is essential that the relative biological effectiveness (RBE) of neutrons is adequately evaluated if a study is to serve as a reference for cancer risk. However, the relatively small neutron component hampered the direct estimation of RBE in LSS data. To circumvent this problem, several strategies have been attempted, including dose-independent constant RBE, dose-dependent variable RBE, and dependence on the degrees of dominance of intermingled γ-rays. By surveying the available literature, we tested the chromosomal RBE of neutrons as the biological endpoint for its equivalence to the microdosimetric quantities obtained using a tissue-equivalent proportional counter (TEPC) in various neutron fields. The radiation weighting factor, or quality factor, Qn, of neutrons as expressed in terms of the energy dependence of the maximum RBE, RBEm, was consistent with that predicted by the TEPC data, indicating that the chromosomally measured RBE was independent of the magnitude of coexisting γ-rays. The obtained neutron RBE, which varied with neutron dose, was confirmed to be the most adequate RBE system in terms of agreement with the cancer incidence in A-bomb survivors, using chromosome aberrations as surrogate markers. With this RBE system, the cancer risk in A-bomb survivors as expressed in unit dose of reference radiation is equally compatible with Hiroshima and Nagasaki cities, and may be potentially applicable in other cases of human radiation exposure.

Serum lipidomic analysis from mixed neutron/X-ray radiation fields reveals a hyperlipidemic and pro-inflammatory phenotype

“…As neutrons have a high relative biological effectiveness (RBE), a low dose can lead to a significant biological effect. It has been calculated that the RBE in a mixed field may only be primarily dependent on the neutron dose and may be higher with decreasing neutron dose 8 . Therefore, a large population that is shielded in buildings or is situated at a distance from the epicenter where the neutrons may be less can still have a significant physiological response.…”

Modelling the influence of radiosensitivity on development of second primary cancer in out-of-field organs following proton therapy for paediatric cranial cancer

“…As such, the cancer risks obtained from A-bomb survivors from Hiroshima/Nagasaki, may potentially be more applicable to the PT case presented in our study, as they include exposure to neutrons, and may therefore more accurately represent risks in relation to SPC due to neutron out-of-field doses. 30 …”

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

“…Thus, when they are absorbed into a stable atom, they commonly cause indirect ionization. This makes them unstable and consequently emit other types of ionizing radiation [19]. After neutrons strike the hydrogen nuclei, proton radiation (fast protons) is produced.…”