Design and evaluation of closed-loop feedback control of minimum temperatures in human intracranial tumours treated with interstitial hyperthermia

Abstract

The dynamic nature of blood flow during hyperthermia therapy has made the control of minimum tumour temperature a difficult task. The paper presents initial studies of a novel approach to closed-loop control of local minimum tissue temperatures utilising a newly developed estimation algorithm for use with conductive interstitial heating systems. The local minimum tumour temperature is explicitly estimated from the power required to maintain each member of an array of electrically heated catheters at a known temperature, in conjunction with a new bioheat equation-based algorithm to predict the 'droop' or fractional decline in tissue temperature between heated catheters. A closed loop controller utilises the estimated minimum temperature near each catheter as a feedback parameter, which reflects variations in local blood flow. In response the controller alters delivered power to each catheter to compensate for changes in blood flow. The validity and stability of this estimation/control scheme were tested in computer simulations and in closed-loop control of nine patient treatments. The average estimation error from patient data analysis of 21 sites at which temperature was independently measured (three per patient) was 0.0 degree C, with a standard deviation of 0.8 degree C. These results suggest that estimation of local minimum temperature and feedback control of power delivery can be employed effectively during conductive interstitial heat therapy of intracranial tumours in man.

Tumor Selective Hyperthermia Induced by Short-Wave Capacitively-Coupled RF Electric-Fields

“…In the1980s the synergy between hyperthermia and radiation was studied in clinical protocols. However, the initial enthusiasm subsided due to the lack of tumor selective hyperthermia delivery systems and difficulties in real-time temperature control [4]–[6]. Over the past decade, advances in nanotechnology, molecular biology, and cancer research have set the path for the development of much more effective, tumor selective, non-invasive nano-hyperthermia systems.…”

Homologous recombination research is heating up and ready for therapy

“…The precise mechanism of action has remained obscure, but hyperthermia appears to be toxic, particularly in the S phase of the cell cycle (3,4). In the 1980s, radiation oncology departments around the world all constructed hyperthermia units, but they were never fully developed for the treatment of deep-seated tumors, because maintaining hyperthermia was a major technical challenge secondary to tumor blood flow being an effective cooling mechanism (5)(6)(7). If the technological issues could be overcome, this therapeutical approach would still have substantial merit.…”

Structure and stability analysis of a Takagi-Sugeno fuzzy PI controller with application to tissue hyperthermia therapy

“…where K, which is constant gain of the model, is in the range 0.12-24.6°C/W and T, which is fixed time constant, is in the range 43-2570 s. The value of time delay varies from patient to patient (typically 10-70 s) and, for typical patients, it is 45 s. The previous study [3] indicates that the parameter values for typical patients are: K:1.1, T:250 and :45 and we use these values as nominal values in the following fuzzy control system design. We emphasize that in medical applications, control system stability needs to be rigorously guaranteed before the system can clinically be implemented.…”

“…Numeric solution takes prohibitively long time. For control simulation study, a linear first-order model with a time delay may be used, which approximates the bio-heat partial differential equation reasonably well [3]. The model is…”