Long-term epidemiological studies of atomic bomb survivors in Hiroshima and Nagasaki: study populations, dosimetry and summary of health effects

Low-dose radiations derived from cone-beam CT induce transient DNA damage and persistent inflammatory reactions in stem cells from deciduous teeth

OBJECTIVES

Cone-beam CT (CBCT), a radiographic tool for diagnosis, treatment, and follow-up in dental practice, was introduced also in pediatric radiology, especially orthodontics. Such patients subjected to repetitive X-rays examinations may receive substantial levels of radiation doses. Ionizing radiation (IR), a recognized carcinogenic factor causing DNA double-strand breaks (DSBs) could be harmful to undifferentiated cells such as dental pulp stem cells (DPSCs) since inaccurately repaired or unrepaired DSBs may lead to malignant transformation. The H2AX and MRE11 proteins generated following DSBs formation and pro-inflammatory cytokines (CKs) secreted after irradiation are relevant candidates to monitor the cellular responses induced by CBCT.

METHODS

DPSCs were extracted from human exfoliated deciduous teeth and their phenotype was assessed by immunocytochemistry and flow-cytometry. Cells were exposed to IR doses: 5.4-107.7 mGy, corresponding to 0.5-8 consecutive skull exposures, respectively. H2AX and MRE11 were detected in whole cells, while IL-1α, IL-6, IL-8, TNFα in supernatants, using enzyme-linked immunosorbent assay (ELISA) at different time points after exposure.

RESULTS

The phosphorylation level of H2AX in DPSCs increased considerably at 0.5 h after exposure (p < 0.001 for 3, 5, 8 skull exposures and p < 0.05 for 1 skull exposure, respectively). MRE11 response could only be detected for the highest IR dose (p < 0.001) in the same interval. CKs secretion increased upon CBCT exposure according to doses and time.

CONCLUSIONS

The DPSCs exposure to CBCT induces transient DNA damage and persistent inflammatory reaction in DPSCs drawing the attention on the potential risks of IR exposures and on the importance of dose monitoring in pediatric population.

Lung, Laryngeal and Other Respiratory Cancer Incidence among Japanese Atomic Bomb Survivors: An Updated Analysis from 1958 through 2009

The Life Span Study (LSS) of Japanese atomic bomb survivors is comprised of a large, population-based cohort offering one of the best opportunities to study the relationship between exposure to radiation and incidence of respiratory cancers. Risks of lung, laryngeal and other cancers of the respiratory system were evaluated among 105,444 LSS subjects followed from 1958 to 2009. During this period, we identified 2,446 lung, 180 laryngeal and 115 other respiratory (trachea, mediastinum and other ill-defined sites) first primary incident cancer cases. Ten additional years of follow-up, improved radiation dose estimates, revised smoking data, and updated migration information were used to investigate the joint effects of radiation and smoking using Poisson regression methods. For nonsmokers, the sex-averaged excess relative risk per Gy (ERR/Gy) for lung cancer (at age 70 after radiation exposure at age 30) was estimated as 0.81 (95% CI: 0.51, 1.18) with a female-to-male ratio of 2.83. There was no evidence of curvature in the radiation dose-response relationship overall or by sex. Lung cancer risks increased with pack-years of smoking and decreased with time since quitting smoking at any level of radiation exposure. Similar to the previously reported study, which followed cohort members through 1999, the ERR/Gy for lung cancer was significantly higher for low-to-moderate smokers than for heavy smokers, with little evidence of any radiation-associated excess risk in heavy smokers. Of 2,446 lung cancer cases, 113 (5%) could be attributed to radiation exposure. Of the 1,165 lung cancer cases occurring among smokers, 886 (76%) could be attributed to smoking. While there was little evidence of a radiation effect for laryngeal cancer, a nonsignificantly elevated risk of other respiratory cancers was observed. However, significant smoking effects were observed for both laryngeal (ERR per 50 pack-years = 23.57; 95% CI: 8.44, 71.05) and other respiratory cancers (ERR per 50 pack-years = 1.21; 95% CI: 0.10, 3.25).