Umesh H. Patel

A computer-based, automated, telephonic system to monitor patient progress in the home setting

In this report we describe an automated, telephonic system to monitor the progress of patients convalescing at home. The system includes a computerized central station that is capable of automated voice communication over the telephone, using voice reproduction, and touch-tone recognition. Peripheral hardware in multiple monitored homes need include only a touch-tone telephone, but may also be augmented by inexpensive, rudimentary diagnostic aids, such as a scale for body weight, a thermometer, or a blood pressure cuff and manometer. Current central hardware includes a NeXT computer, a fax modem, and a specialized telecommunications modem developed specifically for voice telecommunication using the NeXT. The central station acts like a robotic nurse in that it asks patients a series of questions and records the responses. The subjective questions to be asked are patient individualized and pre-selected by the physician from a question menu including items targeted specifically for the patients disease or condition. In addition, clinical data such as body weight, blood pressure, and body temperature obtained from in-home diagnostic aids may be transmitted to the central station over the telephone using touch tones. The time-of-day and frequency of calling are pre-selectable, according to the patients preference and clinical status. Data obtained by the central station can be easily accessed by the duty nurse via menu driven software. Reports depicting significant responses as a function of time are generated in graphical format to facilitate rapid identification of adverse trends. Hard copy reports can be dispersed directly by fax. Results from a pilot study show patients with cardiac disease readily use the system without difficulty or complaints. In one patient a five pound increase in body weight was detected, which prompted the patients cardiologist to adjust his medication. In this way automated telephone follow-up can provide early detection of complications before they become severe, making the home environment safer and more secure for convalescence and contributing to reduced health-care costs.

Effective Estimation and Computer Control of Minimum Tumour Temperature During Conductive Interstitial Hyperthermia

The goal of heat therapy in the treatment of malignant disease is to raise the temperature of all neoplastic tissue to a cytotoxic temperature for a predetermined period of time. This seemingly simple task has proved difficult in vivo in part because of non-uniform power absorption and in part because of non-homogeneous and time-varying tumour blood flow. We have addressed this difficulty first by utilizing the conceptually simple technique of conductive interstitial hyperthermia, in which the tumour is warmed by multiple, electrically heated catheters, and second by implementing on-line control of minimum tumour temperatures near each catheter, estimated on the basis of the steady-state ratio of catheter power to catheter temperature rise. This report presents an analysis of the accuracy, precision, and stability of the on-line minimum temperature estimation/control technique for 22 patients who received 31 separate courses of conductive interstitial hyperthermia for the treatment of malignant brain tumours, and in whom temperature was monitored independently by 12-16 independent sensors per patient. In all patients the technique was found to accurately and precisely estimate and control the local minimum temperatures. Comparison of measured and estimated temperatures revealed a mean difference of 0.0 +/- 0.4 degrees C for those sensors within 1.0 mm of the expected location for minimum temperatures. This technique therefore offers an attractive method for controlling hyperthermia therapy-even in the presence of time varying local blood flow.

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

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 mated 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 closedloop control of nine patient treatments. The average estimation error from patient data 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°C, with a standard deviation of 0·8°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.

Computer-aided design and evaluation of novel catheters for conductive interstitial hyperthermia

Conductive interstitial heating is a modality in which heating elements are implanted directly into the treated tissue. One implementation of such therapy employs electrically heated catheters that are implanted in staggered, parallel rows. To explore strategies for maximising the uniformity of tissue temperature distributions achieved with heated catheters, a two-dimensional computer model with cylindrical co-ordinates was used to evaluate radially and longitudinally the temperature distributions produced by a typical interior catheter surrounded by other similar catheters. Insights from the computer model led to new designs for catheters containing multiple heating elements that produced more uniform thermal distributions, eliminating previous ‘cold spots’ within the treatment volume located near the ends of the catheter. The new catheter designs also include compartments for the optional placement of radioactive seeds for simultaneous thermoradiotherapy.

Development of a rapidly computable descriptor of prostate tissue temperature during transurethral conductive heat therapy for benign prostate hyperplasia

Benign prostate hyperplasia (BPH) is a condition in older men in which the mass of tissue in the prostate gland gradually increases over the course of many years, ultimately leading to urinary outflow obstruction. Current treatment of this condition is to surgically remove the obstructing tissue. One novel alternative therapy being studied is transurethral thermocoagulation of excessive prostatic mass. In this approach, a heat-emitting catheter is placed in the prostatic urethra, and the intraprostatic segment of the catheter is heated to temperatures above 60°C for one hour. Two-dimensional cylindrical-co-ordinate computer simulations of this treatment modality were run to model resultant temperature distributions within the prostate gland and surrounding tissues. The simulations revealed that resultant tissue temperature changes were related directly to the power delivered to the catheter and inversely to the rate of blood perfusion. Further analysis of the temperature profiles produced a rapidly computable predictor of tissue temperature in the radial dimension. Using the predictor, a ‘kill radius’ around the prostatic urethra can be easily computed on-line, during treatment, from clinically available data, catheter, power and catheter temperature. The computed kill radius may serve as a useful predictor of the extent of thermal devitalisation of unwanted obstructing tissue and the long-term success of the treatment in relieving urinary outflow obstruction without surgery.

Evidence of changes in regional blood perfusion in human intracranial tumours during conductive interstitial hyperthermia

Human intracranial tumours were treated using local heat therapy produced by surgically implanted catheters containing local resistive heating elements. Changes in local tumor blood flow were assessed indirectly from an algorithm based on the bioheat transfer equation. The algorithm used the ratio of catheter power to catheter temperature rise to estimate regional blood perfusion. Local heat therapy produced consistent reductions in local apparent perfusion. Changes in apparent regional perfusion occurred in intriguing patterns that gave clues to possible vascular events of therapeutic significance.

Droop: a rapidly computable descriptor of local minimum tissue temperature during conductive interstitial hyperthermia

Although the goal of local hyperthermia therapy for cancer is to elevate the temperature of a tumour to cytotoxic levels, without the presence of ‘cold spots’, varying blood flow has made the achievement of consistent, therapeutic temperature distributions extraordinarily difficult. The paper presents a novel approach to estimating local minimum tumour temperatures during conductive interstitial hyperthermia which facilitates identification and elimination of cold spots. Conductive interstitial hyperthermia is modelled mathematically for a parallel array of implanted, electrically heated catheters which warms the treated tissue by thermal conduction and blood perfusion. Computer simulations employing the bioheat transfer equation reveal a predictive relationship between implanted catheter temperature, catheter power, implantation geometry and local minimum tumour temperature. Formulation of this relationship in terms of a parameter named ‘droop’ allows estimation of local minimum intratumoural temperatures from individual catheter temperature and power. Computer simulations are also performed to determine the sensitivity of the droop-based estimator to variations in properties of the tissue and catheters. Generally, variations in geometry or thermal properties of about 10 per cent cause estimation errors of less than 1°C in magnitude. These results suggest that online estimates of thermal ‘droop’ may provide a practical route to more consistent control of intratumoural minimum temperature during conductive interstitial heat therapy.