六、结语
辐射广泛存在于我们的生活中，主要来源包括天然辐射和人为辐射，其中较易对人体造成损害的是来源于人为辐射的电离辐射。电离辐射是指能使受照射物质发生电离反应的辐射，包括直接电离辐射和间接电离辐射。电离辐射可造成人体DNA难以修复的损伤，然后影响DNA的转录、蛋白质的表达等，进而影响人体细胞的正常代谢和功能，最终导致相应组织器官的结构异常或功能障碍，甚至导致恶性肿瘤的发生。而甲状腺癌是内分泌系统最常见的恶性肿瘤之一，虽然其发病原因尚未有定论，但辐射是目前唯一公认的致甲状腺癌发病的重要原因之一。其中，最能证明甲状腺癌发病与辐射之间关系密切的证据是切尔诺贝利核电站事故。该事故发生后，儿童及青少年甲状腺癌的发病率急剧升高，其原因可能与儿童或青少年甲状腺摄入环境中的放射性131I剂量较多及其甲状腺体积较小以致所受辐射面积较大有关。而目前成人的甲状腺癌发病与辐射之间尚未发现有明确的关联，但过多的辐射暴露有可能引起甲状腺癌的发生的危险度增加。所以，我们要注意保护好甲状腺，尽量避免不必要的辐射暴露，加强辐射防护意识，尤其是儿童及青少年。但面对辐射时，也不必过于恐慌，人体对辐射有一定的耐受力，不同人群都有一定的辐射剂量限值，控制所受辐射剂量在该限值内，则辐射导致的甲状腺癌或其他肿瘤性病变的发生率是相当低的。因此，对于必要的放射性医疗诊断检查或治疗，如131I治疗Graves甲亢和DTC是合理的、正当的、最优的，利大于弊时，是可以接受的。
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附：放射剂量单位
Ci（居里）或Bq（贝克）为放射性活度单位，常用的有Ci、mCi、μCi、Bq、kBq、MBq、GBq。
单位换算关系：
1Ci=1.0×103mCi=1.0×106μCi，
1GBq=1.0×103MBq=1.0×106kBq=1.0×109Bq，
1Ci=3.7×1010Bq=37GBq，
1mCi=3.7×107Bq=37MBq，
1μCi=3.7×104Bq=37kBq，
1Bq=2.703×10-11Ci=2.703×10-8mCi
=2.703×10-5μCi；
Gy（戈瑞）为吸收剂量单位，常用的有Gy、mGy、μGy。
单位换算关系：1Gy=1.0×103mGy=1.0×106μGy。
Sv（希沃特）为效应剂量单位（当量剂量单位），常用的有Sv、mSv、μSv。
单位换算关系：1Sv=1.0×103mSv=1.0×106μSv；
R（伦琴）或C/kg（库仑/千克）为照射剂量单位，常用的有R、mR、μR、C/kg、mC/kg、nC/kg。
单位换算关系：
1R=1.0×103mR=1.0×106μR，
1C/kg=1.0×103mC/kg=1.0×106nC/kg，
1R=2.58×10-4C/kg，
1μR=0.258nC/kg，
1nC/kg=3.876μR≈4μR。