A self-tuning adaptive controller for 3-D image-guided ultrasound cancer therapy

Thermal dose feedback control systems applied to magnetic nanoparticle hyperthermia

Clinical magnetic nanoparticle hyperthermia therapy (MNHT) requires controlled energy deposition to achieve a prescribed tumor thermal dose. The objective of this work is to design a thermal dose feedback control to deliver prescribed Cumulative Equivalent Minutes at 43 [°C] (CEM43) based on values at selected tumor boundary points. Constraints were imposed to maintain the maximum treatment temperature below 60 [°C] and the tumor boundary at ∼ 43 [°C]. The controller was designed by performing an integrated system dynamic - finite element analysis. Finite element-bioheat transfer (FE-BHT) simulations were performed on a computational phantom developed from the imaging data of a de-identified human head divided into voxels representing the skull, cerebrospinal fluid (CSF), brain, tumor, and ventricles. A uniform distribution of magnetic nanoparticles (MNPs) in an ellipsoid was used to represent MNPs in the phantom tumor. The MNP distribution was subdivided into three domains to simulate the steerable spatially confined heating region during MNHT. Proportional-integral-derivative (PID) control and model predictive control (MPC) were explored. Regions of the phantom tumor that were undertreated during the simulated MNHT were selectively heated by adjusting the heating volume to improve the tumor coverage index (CI; tumor volume ≥ CEM43 of 20 [min]). Results show that steerable spatially confined heating improves CI by ∼15%. MPC achieves CI of 80% faster than PID (67 [min] vs. 80 [min]). Simulations demonstrated the feasibility of automated control to deliver tumor conformal thermal doses using steerable spatially confined heating.

Catheter-based ultrasound technology for image-guided thermal therapy: current technology and applications

Catheter-based ultrasound (CBUS) is applied to deliver minimally invasive thermal therapy to solid cancer tumours, benign tissue growth, vascular disease, and tissue remodelling. Compared to other energy modalities used in catheter-based surgical interventions, unique features of ultrasound result in conformable and precise energy delivery with high selectivity, fast treatment times, and larger treatment volumes. We present a concise review of CBUS technology being currently utilized in animal and clinical studies or being developed for future applications. CBUS devices have been categorised into interstitial, endoluminal and endovascular/cardiac applications. Basic applicator designs, site-specific evaluations and possible treatment applications have been discussed in brief. Particular emphasis has been given to ablation studies that incorporate image guidance for applicator placement, therapy monitoring, feedback control, and post-procedure assessment. Examples of devices included here span the entire spectrum of the development cycle from preliminary simulation-based design studies to implementation in clinical investigations. The use of CBUS under image guidance has the potential for significantly improving precision and applicability of thermal therapy delivery.

Development of robust/predictive control strategies for image-guided ablative treatments using a minimally invasive ultrasound applicator

PURPOSE

One important challenge in image-guided ablative therapies is the effect of heat diffusion which can cause damage to surrounding organs and limit the ability to achieve a conformal pattern of thermal damage. Furthermore, tissue properties such as perfusion and energy absorption can be dynamic and difficult to measure. This paper attempts to address these problems by proposing new control methods.

MATERIALS AND METHODS

A novel predictive approach was developed to compensate for the effect of heat diffusion using a minimally invasive rotating ultrasound heating applicator for ablative therapy. This method can be merged into any closed-loop control strategy. A binary controller, a previously developed adaptive proportional-integral controller, and a model reference adaptive controller were employed and compared, all with the predictive element incorporated. The reason for choosing these controllers was that none of them needed a model of the tissue or exact values of their parameters.

RESULTS

The effectiveness of these controllers was demonstrated through both simulation and experimental studies. The results were consistent and demonstrated equivalent performance between controllers.

CONCLUSIONS

The dominant influence on radial targeting accuracy was the prediction element described in this paper. A binary controller with a predictive element may provide the best balance of performance and simplicity for this application.