Abstract

Therapeutic temperature distributions during hyperthermia treatments are very difficult to maintain (e.g., 41.5 to 43°C for 45 to 60 min.) due to many heat removal/loss mechanisms. Thermoregulatory responses of the human body are efficacious in preserving and re-establishing normothermic conditions, and are considered to be the main cause of temperature non-uniformities through effected changes in blood perfusion and blood flow in large vessels. From the very beginning of hyperthermia technology development temperature feedback control systems (temperature controllers) have been proposed as a way to counterbalance thermoregulation and improve thermal doses. Only a few controllers, however, have been thoroughly tested numerically, experimentally, and most importantly, clinically. In this paper the proportional-integral-derivative bang-bang (PIDBB) controller of Lin et al. (1990), originally designed for a scanned focused ultrasound system for deep localized hyperthermia, was applied numerically to a scanned dual-frequency planar ultrasound system for chest wall hyperthermia. It was found that PIDBB controller with the optimal parameter values as determined by Lin et al. (1990) performed satisfactorily in controlling temperatures in superficial chest wall volumes.

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