195 1年加拿大Johns成功研制了60 Co远距离治疗机 ,195 2年开始投入临床应用 ,这标志着放疗“千伏”时代的结束和“兆伏”时代的开始 ,皮肤毒性明显减轻 ,放疗适应证进一步扩大 ,疗效也明显提高 ,如鼻咽癌患者的 5年生存率从 2 0 %～ 2 5 %提高到了 40 %～ 5 0 % [1] 。我们就6 195 One year Johns, Canada, successfully developed the 60Co teletherapy machine and began clinical application in 1952. This marked the end of the “kilovolt” era of radiotherapy and the beginning of the “megavolt” era. The skin toxicity was significantly reduced and the radiotherapy was adapted Evidence to further expand the curative effect has also significantly improved, such as 5-year survival rate of patients with nasopharyngeal carcinoma from 20% to 25% to 40% to 50% [1]. We will 6