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      Residential Radon and Brain Tumour Incidence in a Danish Cohort

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          Abstract

          Background

          Increased brain tumour incidence over recent decades may reflect improved diagnostic methods and clinical practice, but remain unexplained. Although estimated doses are low a relationship between radon and brain tumours may exist.

          Objective

          To investigate the long-term effect of exposure to residential radon on the risk of primary brain tumour in a prospective Danish cohort.

          Methods

          During 1993–1997 we recruited 57,053 persons. We followed each cohort member for cancer occurrence from enrolment until 31 December 2009, identifying 121 primary brain tumour cases. We traced residential addresses from 1 January 1971 until 31 December 2009 and calculated radon concentrations at each address using information from central databases regarding geology and house construction. Cox proportional hazards models were used to estimate incidence rate-ratios (IRR) and 95% confidence intervals (CI) for the risk of primary brain tumours associated with residential radon exposure with adjustment for age, sex, occupation, fruit and vegetable consumption and traffic-related air pollution. Effect modification by air pollution was assessed.

          Results

          Median estimated radon was 40.5 Bq/m 3. The adjusted IRR for primary brain tumour associated with each 100 Bq/m 3 increment in average residential radon levels was 1.96 (95% CI: 1.07; 3.58) and this was exposure-dependently higher over the four radon exposure quartiles. This association was not modified by air pollution.

          Conclusions

          We found significant associations and exposure-response patterns between long-term residential radon exposure radon in a general population and risk of primary brain tumours, adding new knowledge to this field. This finding could be chance and needs to be challenged in future studies.

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          Most cited references29

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          Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study

          Summary Background Although CT scans are very useful clinically, potential cancer risks exist from associated ionising radiation, in particular for children who are more radiosensitive than adults. We aimed to assess the excess risk of leukaemia and brain tumours after CT scans in a cohort of children and young adults. Methods In our retrospective cohort study, we included patients without previous cancer diagnoses who were first examined with CT in National Health Service (NHS) centres in England, Wales, or Scotland (Great Britain) between 1985 and 2002, when they were younger than 22 years of age. We obtained data for cancer incidence, mortality, and loss to follow-up from the NHS Central Registry from Jan 1, 1985, to Dec 31, 2008. We estimated absorbed brain and red bone marrow doses per CT scan in mGy and assessed excess incidence of leukaemia and brain tumours cancer with Poisson relative risk models. To avoid inclusion of CT scans related to cancer diagnosis, follow-up for leukaemia began 2 years after the first CT and for brain tumours 5 years after the first CT. Findings During follow-up, 74 of 178 604 patients were diagnosed with leukaemia and 135 of 176 587 patients were diagnosed with brain tumours. We noted a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy 0·036, 95% CI 0·005–0·120; p=0·0097) and brain tumours (0·023, 0·010–0·049; p<0·0001). Compared with patients who received a dose of less than 5 mGy, the relative risk of leukaemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51·13 mGy) was 3·18 (95% CI 1·46–6·94) and the relative risk of brain cancer for patients who received a cumulative dose of 50–74 mGy (mean dose 60·42 mGy) was 2·82 (1·33–6·03). Interpretation Use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the first scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. Nevertheless, although clinical benefits should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible and alternative procedures, which do not involve ionising radiation, should be considered if appropriate. Funding US National Cancer Institute and UK Department of Health.
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            Extrapulmonary translocation of ultrafine carbon particles following whole-body inhalation exposure of rats.

            Studies with intravenously injected ultrafine particles have shown that the liver is the major organ of their uptake from the blood circulation. Measuring translocation of inhaled ultrafine particles to extrapulmonary organs via the blood compartment is hampered by methodological difficulties (i.e., label may come off, partial solubilization) and analytical limitations (measurement of very small amounts). The objective of our pilot study was to determine whether ultrafine elemental carbon particles translocate to the liver and other extrapulmonary organs following inhalation as singlet particles by rats. We generated ultrafine (13)C particles as an aerosol with count median diameters (CMDs) of 20-29 nm (GSD 1.7) using electric spark discharge of (13)C graphite electrodes in argon. Nine Fischer 344 rats were exposed to these particles for 6 h. in whole-body inhalation chambers at concentrations of 180 and 80 microg/m(3); 3 animals each were killed at 0.5, 18, and 24 h postexposure. Six unexposed rats served as controls. Lung lobes, liver, heart, brain, olfactory bulb, and kidney were excised, homogenized, and freeze-dried for analysis of the added (13)C by isotope ratio mass spectrometry. Organic (13)C was not detected in the (13)C particles. The (13)C retained in the lung at 0.5 h postexposure was about 70% less than predicted by rat deposition models for ultrafine particles, and did not change significantly during the 24-h postexposure period. Normalized to exposure concentration, the added (13)C per gram of lung on average in the postexposure period was approximately 9 ng/g organ/microg/m(3). Significant amounts of (13)C had accumulated in the liver by 0.5 h postinhalation only at the high exposure concentration, whereas by 18 and 24 h postexposure the (13)C amount of the livers of all exposed rats was about fivefold greater than the (13)C burden retained in the lung. No significant increase in (13)C was detected in the other organs which were examined. These results demonstrate effective translocation of ultrafine elemental carbon particles to the liver by 1 d after inhalation exposure. Translocation pathways include direct input into the blood compartment from ultrafine carbon particles deposited throughout the respiratory tract. However, since predictive particle deposition models indicate that respiratory tract deposits alone may not fully account for the hepatic (13)C burden, input from ultrafine particles present in the GI tract needs to be considered as well. Such translocation to blood and extrapulmonary tissues may well be different between ultrafine carbon and other insoluble (metal) ultrafine particles.
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              Ionizing radiation and the risk of brain and central nervous system tumors: a systematic review.

              Although exposure to moderate-to-high doses of ionizing radiation is the only established environmental risk factor for brain and CNS tumors, it is not clear whether this relationship differs across tumor subtypes, by sex or age at exposure, or at the low-to-moderate range of exposure. This systematic review summarizes the epidemiologic evidence on the association between ionizing radiation exposure and risk of brain/CNS tumors. Articles included in this review estimated radiation exposure doses to the brain and reported excess relative risk (ERR) estimates for brain/CNS tumors. Eight cohorts were eligible for inclusion in the analysis. Average age at exposure ranged from 8 months to 26 years. Mean dose to the brain ranged from 0.07 to 10 Gy. Elevated risks for brain/CNS tumors were consistently observed in relation to ionizing radiation exposure, but the strength of this association varied across cohorts. Generally, ionizing radiation was more strongly associated with risk for meningioma compared with glioma. The positive association between ionizing radiation exposure and risk for glioma was stronger for younger vs older ages at exposure. We did not observe an effect modification on the risk for meningioma by sex, age at exposure, time since exposure, or attained age. The etiologic role of ionizing radiation in the development of brain/CNS tumors needs to be clarified further through additional studies that quantify the association between ionizing radiation and risk for brain/CNS tumors at low-to-moderate doses, examine risks across tumor subtypes, and account for potential effect modifiers.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2013
                16 September 2013
                : 8
                : 9
                : e74435
                Affiliations
                [1 ]Diet, Genes and Environment, Danish Cancer Society Research Centre, Copenhagen, Denmark
                [2 ]Construction and Health, Danish Building Research Institute, Aalborg University, Aalborg, Denmark
                [3 ]Department of Public Health, Faculty of Health Sciences, Copenhagen University, Copenhagen, Denmark
                [4 ]Center for Nuclear Technologies, Technical University of Denmark, Roskilde, Denmark
                [5 ]Geological Survey of Denmark and Greenland, Copenhagen, Denmark
                [6 ]National Institute of Radiation Protection, Herlev, Denmark
                [7 ]Department of Environmental Science, Aarhus University, Aarhus, Denmark
                Indiana University, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: EVB ORN. Performed the experiments: EVB CEA OH. Analyzed the data: EVB PG KU CP OH. Contributed reagents/materials/analysis tools: EVB ZJA CEA PG. Wrote the paper: EVB ZJA CEA CP PG KU OH SL ORN.

                Article
                PONE-D-13-17313
                10.1371/journal.pone.0074435
                3774631
                24066143
                b7babed3-c586-4f78-993d-9fba84e445ce
                Copyright @ 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 29 April 2013
                : 31 July 2013
                Page count
                Pages: 7
                Funding
                This work was supported by a Research Grant from The Danish Medical Research Council (Grant number: 09 064754). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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