3.chapter2 deices for radiation therapy3.chapter2 devices for radiation therapy3.chapter2 devices for radiation therapy3.chapter2 devices for radiation therapy.ppt

Devices for radiation therapy 放射治疗设备 Devices for radiation therapy Kilovoltage units Cobalt-60 units Linear accelerator 近距离治疗机 模拟定位机 立体定向照射设备 Kilovoltage units Up to about 1950, most of the external beam radiotherapy was carried out with x-rays generated at voltage up to 300kVp. Subsequent development of higher-energy machines and the increasing popularity of the cobalt-60 units in the 1950s and the 1960s resulted in a gradual demise of the conventional kilovoltage machines. Kilovoltage units However, these machines have not completely disappeared. Even in the present era of the megavoltage beams, there is still some use for the lower-energy beams, especially in the treatment of superficial skin lesions. Kilovoltage units X射线的产生原理 Characteristic X-rays Bremsstrahlung （braking radiation） X射线治疗机的基本结构 HVL（half value layer） 定义 使用滤过板，吸收软光子，硬化射线（能量、复合滤过板） Kilovoltage units X射线治疗机的分类 Contact therapy：加速势能20~50KV，治疗距离即靶到皮肤距离10cm或更小，治疗深度1~2mm Superficial therapy：加速势能50~150KV, HVL为1~8mm铝，治疗距离10~30cm，治疗深度一般到5mm Deep therapy （orthovoltage therapy）：加速势能150~300KV，治疗距离30~40cm，HVL约为1~3mm铜，治疗深度一般到2cm Cobalt-60 units The cobalt-60 source is produced by irradiating ordinary stable Co-59 with neutrons in a reactor. The Co-60 source , usually in the form of a solid cylinder, discs, or pallets, is contained inside a stainless-steel capsule and sealed by welding. This capsule is placed into another steel capsule which is again sealed by welding. The double-welded seal is necessary to prevent any leakage of the radioactive material. Cobalt-60 teletherapy unit manufactured by Theratronics (now MDS-Nordion), Ottawa, Canada: left – actual photo, right – schematic diagram depicted on a postage stamp issued by Canada Post in 1988 in honour of Dr. Harold E. Johns who invented the cobalt-60 unit in the 1950s. Structure of Cobalt-60 units Co-60治疗机一般由以下部分组成： 一个密封的Co-60放射源 一个源容器及防护机头 具有开关的遮线器装置 具有定向线束的准直器 放射源半影 支持机头的治疗机架，用以调节线束方向 治疗床 计时器及运动控制系统 辐射安全及连锁系统 Cobalt-60 units Co-60 γ 射线的平均能量