Ryan T P, Miller W
Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755.
J Biomed Eng. 1989 Mar;11(2):130-2. doi: 10.1016/0141-5425(89)90122-2.
In many cancer treatment facilities where hyperthermia treatments are performed, there is a need to split a single channel microwave source into multiple, individually controllable channels. In the application reported here, microwave power is alternately switched between active and passive elements for each channel. The active element is either a microwave antenna inside a catheter in tumour tissue or a planar spiral applicator placed superficially, the total power to each channel being pulse width modulated from 1 to 99% of a 1 s duty cycle. The system is computer controlled and is capable of dividing and controlling power to 12 channels. PIN diode switch assemblies control the flow of power in each channel but they must be switched within a few microseconds to avoid failure at the high power levels used in the clinic. A high speed circuit was fabricated and tested to drive each PIN diode switch; the PIN diode switches are turned on in 1.5 microseconds and off in 3.0 microseconds, which meets the specifications for hot switching. The increase in speed over the former driver system is a factor of 5.1 for the on cycle and 1.5 x 10(5) for the off cycle and the maximum power tested in each channel was 80 W for 1 h at random duty cycles between 1 and 99%. The circuit was also tested with 40 W of power at duty cycles of 1, 50 and 99% for 1 h each; no failures or performance decrements were observed. The 12 channel circuit driver has been used for six months of clinical treatments without failure.
在许多开展热疗治疗的癌症治疗机构中，需要将单通道微波源分成多个可单独控制的通道。在本文报道的应用中，微波功率在每个通道的有源元件和无源元件之间交替切换。有源元件要么是肿瘤组织中导管内的微波天线，要么是表面放置的平面螺旋施加器，每个通道的总功率通过脉宽调制，占空比为1秒的1%至99%。该系统由计算机控制，能够将功率分配并控制到12个通道。PIN二极管开关组件控制每个通道中的功率流，但它们必须在几微秒内切换，以避免在临床使用的高功率水平下出现故障。制作并测试了一个高速电路来驱动每个PIN二极管开关；PIN二极管开关在1.5微秒内导通，在3.0微秒内关断，这符合热切换的规格要求。与前一个驱动系统相比，导通周期的速度提高了5.1倍，关断周期提高了1.5×10⁵倍，在每个通道中测试的最大功率为80瓦，在1%至99%的随机占空比下持续1小时。该电路还在占空比为1%、50%和99%的情况下分别以40瓦的功率测试了1小时；未观察到故障或性能下降。12通道电路驱动器已用于临床治疗六个月，无故障发生。
