Development of a new control strategy for 3D MRI-controlled interstitial ultrasound cancer therapy

Purpose: MRI-controlled interstitial ultrasound therapy is being developed as a minimally invasive, image-guided treatment for localized cancers. The method uses an interstitial multielement ultrasound applicator to deliver high-intensity ultrasound energy to tissue in order to achieve thermal coagulation in a target volume. Methods: A new temperature feedback control algorithm incorporating a proportional-integral controller is introduced to tackle a multiple-input single-output control problem arising in MRI-controlled interstitial ultrasound cancer therapy. The inputs to the controller block are the frequency, rotation rate, and applied power of an interstitial applicator and the output is the boundary temperature during treatment. Multiplanar magnetic resonance (MR) thermometry is acquired continuously during heating and used in the feedback control algorithm to achieve spatial control over treatment. Results: The method has been evaluated for prostate cancer treatment as an initial clinical application. Spatial treatment accuracy of a few millimeters is demonstrated in both simulations and experiments with the new controller. The spatial treatment accuracy of the new algorithm is shown to be equivalent or slightly improved over the existing approach implemented for this technology; however, the implementation of the new algorithm is much simpler, and does not involve time-intensive tuning of gain constants. Conclusions: The study demonstrates the potential advantages of a new automatic temperature control system adapted to image guided interstitial ultrasound therapy.