“…In a cohort of 4977 U.S. mound workers potentially exposed to external or internal (polonium-210, plutonium isotopes, or tritium) radiation (mean dose from external radiation: 26.1 mSv; max: 939.1 mSv; mean lung dose from external and internal radiation combined: 100.1 mSv; max: 17.5 Sv; mean liver dose from external and internal radiation: 34.6 mSv; max: 2.3 Sv), the mortality due to diseases of the nervous system was not different from that of the general population, regardless of the radiation status of the workers or the type of radionuclides for those with intakes, but a positive trend was suggested as SMRs increased with increasing categories of occupational cumulative dose primarily due to photons ( p = 0.03) [ 42 ]. In a cohort of 26,328 Los Alamos National Laboratory workers exposed to a combination of photons, neutrons, tritium, and plutonium (among which 17,053 workers were monitored for a combination of external and internal sources for plutonium; brain radiation absorbed dose: mean: 11.6 mGy; max: 760 mGy), Boice et al (2021) reported among the whole cohort a non-significant SMR for nervous system diseases compared with national rates based on 815 deaths, but a borderline significant increase in mortality due to Parkinson’s disease was observed (SMR = 1.16; 95% CI: 1.00, 1.34; n deaths = 193), and a positive dose–response relationship was suggested (ERR at 100 mGy = 0.16; 95% CI: −0.07, 0.40; n deaths = 273) [ 33 ]. In a cohort of 22,377 Mayak workers exposed to chronic IR (mean cumulative dose from external gamma rays absorbed in the brain: 0.46 Gy (max: 8.01 Gy) for men and 0.36 Gy (max: 6.14 Gy) for women), a statistically significant linear association was found between the incidence of Parkinson’s disease and cumulative gamma dose after adjusting for sex and attained age (ERR per Gy = 1.02; 95% CI: 0.59, 1.63; n diseases = 300) [ 12 ].…”