Masse R, Cross F T
CEA, Institut de Protection et de Sûreté Nucléaire, DPS/SPE, Centre d'Etudes de Fontenay aux Roses, France.
Health Phys. 1989;57 Suppl 1:283-9. doi: 10.1097/00004032-198907001-00036.
Improved lung models provide a more accurate assessment of dose from inhalation exposures and, therefore, more accurate dose-response relationships for risk evaluation and exposure limitation. Epidemiological data for externally irradiated persons indicate that the numbers of excess respiratory tract carcinomas differ in the upper airways, bronchi, and distal lung. Neither their histogenesis and anatomical location nor their progenitor cells are known with sufficient accuracy for accurate assessment of the microdosimetry. The nuclei of sensitive cells generally can be assumed to be distributed at random in the epithelium, beneath the mucus and tips of the beating cilia and cells. In stratified epithelia, basal cells may be considered the only cells at risk. Upper-airway tumors have been observed in both therapeutically irradiated patients and in Hiroshima-Nagasaki survivors. The current International Commission on Radiological Protection Lung-Model Task Group proposes that the upper airways and lung have a similar relative risk coefficient for cancer induction. The partition of the risk weighting factor, therefore, will be proportional to the spontaneous death rate from tumors, and 80% of the weighting factor for the respiratory tract should be attributed to the lung. For Weibel lung-model branching generations 0 to 16 and 17 to 23, the Task Group proposes an 80/20 partition of the risk, i.e., 64% and 16%, respectively, of the total risk. Regarding risk in animals, recent data in rats indicate a significantly lower effectiveness for lung-cancer induction at low doses from insoluble long-lived alpha-emitters than from Rn daughters. These findings are due, in part, to the fact that different regions of the lung are irradiated. Tumors in the lymph nodes are rare in people and animals exposed to radiation. The Task Group, therefore, suggests that the total risk to the nodes cannot exceed 1/100th of the total risk to the respiratory tract, which, in turn, leads to an extremely low cancer incidence per unit dose for lymphatic tissue.
改进的肺部模型能更准确地评估吸入性暴露的剂量，从而为风险评估和暴露限制提供更准确的剂量-反应关系。外部照射人群的流行病学数据表明，上呼吸道、支气管和肺远端的呼吸道癌超额病例数有所不同。就其组织发生、解剖位置及其祖细胞而言，目前尚缺乏足够准确的认识，无法准确评估微剂量学。一般认为，敏感细胞的细胞核随机分布在上皮细胞中，位于黏液下方以及纤毛和细胞的顶端。在复层上皮中，基底细胞可能被视为唯一有风险的细胞。在接受治疗性照射的患者以及广岛和长崎幸存者中均观察到上呼吸道肿瘤。当前国际放射防护委员会肺部模型任务组提议，上呼吸道和肺部诱发癌症的相对风险系数相似。因此，风险权重因子的分配将与肿瘤的自然死亡率成正比，呼吸道的权重因子的80%应归因于肺部。对于韦贝尔肺部模型的0至16级分支以及17至23级分支，任务组提议风险分配比例为80/20，即分别占总风险的64%和16%。关于动物中的风险，近期大鼠的数据表明，与氡子体相比，低剂量的不溶性长寿命α发射体诱发肺癌的有效性显著较低。这些发现部分归因于肺部不同区域受到照射。在受辐射的人和动物中，淋巴结中的肿瘤很少见。因此，任务组建议，淋巴结的总风险不能超过呼吸道总风险的1/100，这反过来导致淋巴组织每单位剂量的癌症发病率极低。
