Minimum-Time Thermal Dose Control of Thermal Therapies

Abstract

The problem of controlling noninvasive thermal therapies is formulated as the problem of directly controlling thermal dose of the target. To limit the damage to the surrounding normal tissue, the constraints on the peak allowable temperatures in the selected spacial locations are imposed. The developed controller has a cascade structure with a linear, constrained, model predictive temperature controller in the secondary loop. The temperature controller manipulates the intensity of the ultrasound transducer with saturation constraints, which noninvasively heats the spatially distributed target. The main nonlinear thermal dose controller dynamically generates the reference temperature trajectories for the temperature controller. The thermal dose controller is designed to force the treatment progression at either the actuation or temperature constraints, which is required to minimize the treatment time. The developed controller is applicable to high and low-intensity treatments, such as thermal ablation and thermoradiotherapy. The developed approach is tested using computer simulations for a one-dimensional model of a tumor with constraints on the maximum allowable temperature in the normal tissue and a constrained power output of the ultrasound transducer. The simulation results demonstrate that the proposed approach is effective at delivering the desired thermal dose in a near minimum time without violating constraints on the maximum allowable temperature in healthy tissue, despite significant plant-model mismatch introduced during numerical simulation. The results of in vitro and in vivo validation are reported elsewhere.

Bio-heat transfer analysis during short pulse laser irradiation of tissues

“…It has been found that peak temperature in the range of 60-80°C is required to ensure complete tumor necrosis without any post-treatment trauma [19]. However, it has been also observed that temperature required to kill the tumor tissue depends on the exposure time [20,21]. Robinson et al [22] has predicted that temperature elevation to at least 56°C for 1 s or more should be sufficient to kill cancer cells.…”

Image-based identification of low-dimensional POD models of noninvasive thermal therapies

“…The low-dimensionality of the identified models and image compression is important for the real-time implementation of model-based treatment control system with MRI feedback, especially in the case of computationally expensive controllers, such as optimizing, predictive controllers described in [18], [15], [19], [20].…”

Identification of Reduced-Order Thermal Therapy Models Using Thermal MR Images: Theory and Validation

“…With the available patient- and site-specific heat deposition and dissipation models (collectively, treatment model), the optimization of the treatment plan becomes possible and may include the selection of appropriate applicators, their spatial positioning, and the configuration of the temperature monitoring system. Model-based automatic treatment control systems can provide such advanced functionality as minimization of the treatment time without exceeding the maximum allowable temperature in the normal tissues [5], [6]. …”