游離輻射暴露與非癌症疾病

從二次世界大戰二顆原子彈投擲（日本之廣島與長崎）及核能發電廠意外事故（如美國賓州三哩島核電廠、蘇俄車諾比核電廠等）等受波及之民眾，其健康長期追蹤調查之研究報告，大多數集中於惡性腫瘤之發生率與死亡率，如白血病（leukemia）、再生不良性貧血（aplastic anemia）、臟器癌症（如甲狀腺癌、肺癌、胰臟癌、惡性淋巴瘤、腦瘤、肝癌等）、骨癌，至於非癌症疾病，如心臟血管疾病、腦中風、高血壓、糖尿病、腎臟病、腸胃道疾病、白內障（cataract）、皮膚炎、憂鬱症、創傷後壓力疾患（post-traumatic stress disorder, PTSD）、神經組織病變或畸胎（teratoma）等研究報告相對較少。游離輻射之健康效應，一般可分為兩大類，一為非隨機效應（nonstochastic），另一為隨機效應（stochastic）。非隨機效應指的是受害者疾病嚴重度之進行與接觸劑量大小有關，即有所謂的安全閾值（safety threshold）存在，暴露劑量一旦低於閾值，便不會有任何病變產生；反之，隨機效應則無安全閾值，其發生與否是一種機率（probability），即罹患癌症或基因遭受破壞。一般而言，身體內細胞快速分裂之器官或組織，如骨髓、皮膚、泌尿道黏膜、性腺器官、腸胃道黏膜或口腔黏膜等，對游離輻射最為敏感，即罹病風險相對高。癌症發生之部位則決定於游離輻射源所尋找之標的器官（target organs），如碘-131與甲狀腺、鍶-90與骨頭。非隨機效應可分為急性（acute）與延遲（delayed）兩大類，前者如急性輻射症候群（acute radiation syndrome），即在短時間內接受大劑量暴露，通常會損及腸胃道系統、血液系統及中樞神經系統；延遲效應方面如白內障、皮膚炎。對於無能力修復或恢復能力較慢之標的器官，如眼球晶體和神經組織等，應加以特別防範及保護。國際輻射防護委員會（International Commission on Radiation Protection, ICRP）因此於西元1999年公布年游離輻射暴露安全劑量限值，如一般民眾每年全身輻射暴露劑量應不大於1毫西弗（mSv）（不含天然背景輻射及醫療暴露劑量），而輻射工作人員全身暴露一年不能大於20毫西弗等建議（見表一）。生活環境或職場工作亦可能接觸到游離輻射，如宇宙射線（cosmic rays）、建材釋放之加馬射線gamma(γ)rays、核醫檢測或X-ray照射等，經常上山、下海潛水、飛航搭乘頻繁（台北往返美國西岸一趟約0.09毫西弗）等人，游離輻射暴露劑量會較一般人高（台灣地區每人每年接受天然背景輻射劑量的平均值約為1.6毫西弗）。

關鍵字

非癌症疾病；游離輻射；心血管疾病；白內障

並列摘要

Epidemiologic studies of survivors of the atomic bomb, the Chernobyl accident mostly focused on the cancer mortality, a causative link has long been established between exposure to ionizing radiation and the risk of mortality from many forms of cancer, such as leukemia, thyroid cancer, aplastic anemia, lung cancer, etc. Non-cancer diseases after exposure such as cardiovascular disease, cataract, depression, PTSD, skin disorder, mental retardation are lessly mentioned and discussed. Health effects of ionizing radiation exposure can be divided into two catagories, one is nonstochastic effect; the other stochastic effect. Nonstochastic effect of exposures means that disease severity and progression is associated with the dose amount of radiation, namely it has a safety threshold, there is no harm if exposure dose is below the threshold value. On the contrary, there is no so called safety threshold for stochastic effect, incidence itself is a kind of probability, such cancer or gene defect. In general, body organs with rapid cell turnover rate, such as skin, bone marrow, GI tract mucosa, gonads, etc., are very sensitive to ionizing radiation, hence relatively high risk for morbidity and mortality. For which site cancer may develop, it depends on target organ of irradiation source, for example iodine-131 with thyroid gland, thorium-80 with bone. Nonstochastic effect can be divided into two classes, one is acute type, the other delayed type. Exposed to a very large amount of radiation in a short period may develop acute radiation syndrome, it mostly cause damage to GI tract system, hemato-logical system and central nervous system. For delayed type effect, such as cataract, dermatitis, may develop after a long term exposure .Hence, for those target organs with incapability to repair or slowly recovering characteristics, such as lens, nerve tissues, specific prevention and protection should be roposed in advance.

並列關鍵字

noncancer disease ； ionizing radiation ； cardiovascular disease ； cataract

國際替代計量

游離輻射暴露與非癌症疾病

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