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Biomedical subjects

J W Hand

Publications and source records attributed to J W Hand.

At least 19 recordsLinked to original sources
PubMed1996

Radiotherapy with or without hyperthermia in the treatment of superficial localized breast cancer: results from five randomized controlled trials. International Collaborative Hyperthermia Group.

PURPOSE: Claims for the value of hyperthermia as an adjunct to radiotherapy in the treatment of cancer have mostly been based on small Phase I or II trials. To test the benefit of this form of treatment, randomized Phase III trials were needed. METHODS AND MATERIALS: Five randomized trials addressing this question were started between 1988 and 1991. In these trials, patients were eligible if they had advanced primary or recurrent breast cancer, and local radiotherapy was indicated in preference to surgery. In addition, heating of the lesions and treatment with a prescribed (re)irradiation schedule had to be feasible and informed consent was obtained. The primary endpoint of all trials was local complete response. Slow recruitment led to a decision to collaborate and combine the trial results in one analysis, and report them simultaneously in one publication. Interim analyses were carried out and the trials were closed to recruitment when a previously agreed statistically significant difference in complete response rate was observed in the two larger trials. RESULTS: We report on pretreatment characteristics, the treatments received, the local response observed, duration of response, time to local failure, distant progression and survival, and treatment toxicity of the 306 patients randomized. The overall CR rate for RT alone was 41% and for the combined treatment arm was 59%, giving, after stratification by trial, an odds ratio of 2.3. Not all trials demonstrated an advantage for the combined treatment, although the 95% confidence intervals of the different trials all contain the pooled odds ratio. The greatest effect was observed in patients with recurrent lesions in previously irradiated areas, where further irradiation was limited to low doses. CONCLUSION: The combined result of the five trials has demonstrated the efficacy of hyperthermia as an adjunct to radiotherapy for treatment of recurrent breast cancer. The implication of these encouraging results is that hyperthermia appears to have an important role in the clinical management of this disease, and there should be no doubt that further studies of the use of hyperthermia are warranted.

Breast Neoplasms↗
PubMed1996

Calculation of electrical potentials on the surface of a realistic head model by finite differences.

We present a method for the calculation of electrical potentials at the surface of realistic head models from a point dipole generator based on a 3D finite-difference algorithm. The model was validated by comparing calculated values with those obtained algebraically for a three-shell spherical model. For a 1.25 mm cubic grid size, the mean error was 4.9% for a superficial dipole (3.75 mm from the inner surface of the skull) pointing in the radial direction. The effect of generator discretization and node spacing on the accuracy of the model was studied. Three values of the node spacing were considered: 1, 1.25 and 1.5 mm. The mean relative errors were 4.2, 6.3 and 9.3% respectively. The quality of the approximation of a point dipole by an array of nodes in a spherical neighbourhood did not depend significantly on the number of nodes used. The application of the method to a conduction model derived from MRI data is demonstrated.

Brain↗
PubMed1995

The use of a current sheet applicator array for superficial hyperthermia: incoherent versus coherent operation.

There are a number of potential advantages to be gained by using an array of applicators in hyperthermia treatments compared with single applicator systems. These advantages include the possibility of greater spatial control of power deposition and conformability to nonplanar sites. Arrays of applicators can be driven either coherently or incoherently. In the case of coherent operation, an added advantage is the ability to steer power deposition by varying the phases of the antennas. In this study, we investigated the relative merits of the two modes of operation when a 2 x 2 planar array of current sheet applicators is used. The effective field size (EFS) of the array was calculated using a Gaussian beam representation of the applicators on a layered model in which the fat layer had its thickness varied. Good agreement was obtained between the square of the electric field distribution (E2) and quantitative experimental results. It is shown that when the planar array is used with a fat layer greater than about 2 mm present, it should be driven incoherently as this results in a significantly larger EFS than that obtained when the array is driven coherently.

Humans↗
PubMed1994

Further observations on the measurement of tissue T1 to monitor temperature in vivo by MRI.

Previous results for the measurement of T1 as a means of monitoring temperature have demonstrated a linear calibration with a coefficient of the order of 1.5%/degrees C. We have studied the changes in T1 further, and observe that changes in tissue perfusion are substantial contributors to the effects observed, and that the model of what is happening is complex and may not permit a simple temperature calibration.

Body Temperature↗
PubMed1994

Modeling and observation of temperature changes in vivo using MRI.

Models have been developed for the signal changes occurring in human peripheral muscle after thermal stress for some methods of measuring temperature in vivo. These include the dependency of T1 on temperature, observed by both direct, and magnetization transfer, experiments, and the temperature sensitivity of the diffusion coefficient and the chemical shift of the water proton line. Results show the relative complexity of the T1-dependent models when there are significant variations in, possibly amongst other things, tissue perfusion, and how the predictions made using them match the behavior of the practical values quite well. Using changes in the diffusion coefficient appears less problematic, although there can still be significant errors in temperature calibrations. The problems with this approach are likely to be due to the consequences of anisotropy in tissue.

Adipose Tissue↗
PubMed1993

SAR distributions in interstitial microwave antenna arrays with a single dipole displacement.

The use of interstitial microwave antenna array hyperthermia (IMAAH) as a treatment for cancer, in conjunction with radiation therapy and chemotherapy, has been investigated widely. The heating pattern produced by a coherently phased 915 MHz asymmetric antenna array displays the maximum power deposition in the array center. This paper investigates the effect of variable insertion depth between antennas of an array on the heating patterns produced. The "study" of this heating behavior demonstrates a similar effect to that of the variably phased arrays, showing a shift of the heating peak towards the periphery of the tumor, offering a more simple method for the clinical treatment of such tumors.

Computer Simulation↗
PubMed1992

Guidelines for thermometry in clinical hyperthermia.

High quality thermometry is needed in hyperthermia to (1) ensure safe delivery of adequate therapy and (2) provide the quantitative information needed to develop prognostic parameters which will aid research into planning and dosimetry. Currently, only invasive thermometry which is subject to several sources of artifact is available to address these requirements. This paper summarizes techniques which have been developed to reduce these artifacts to acceptable levels, outlines quality assurance requirements ensuring good practice in the use of invasive thermometry during clinical treatments and ends with a brief discussion of thermometry requirements for control of various hyperthermia systems.

Electromagnetic Fields↗
PubMed1991

Control of specific absorption rate distribution using capacitive electrodes and inductive aperture-type applicators: implications for radiofrequency hyperthermia.

A method of controlling the specific absorption rate (SAR) distribution in radiofrequency hyperthermia is proposed. The superposition of the current density associated with capacitively coupled electrodes and that associated with H-field coupled inductive aperture-type applicators modifies the actual current distribution in the heating material. Using a two-dimensional finite element method, we have shown that "focusing" is possible such that the SAR at the center of a phantom can be adjusted to be approximately twice that in superficial regions, even though the wavelength is considerably greater than the dimensions of the phantom.

Electric Conductivity↗
PubMed1990

Treatment of functional menorrhagia by radiofrequency-induced thermal endometrial ablation.

42 patients were enrolled in a trial of radiofrequency-induced thermal endometrial ablation for the treatment of functional menorrhagia. The radiofrequency electromagnetic energy was delivered via a probe placed within the endometrial cavity. 10 patients received 330 kJ of energy, 10 received 445 kJ, and the other 22 received 660 kJ. 19 (87%) of those receiving the highest dose became amenorrheic or had a considerable reduction in menstrual flow. The procedure is simple and the heat induced in the endometrium does not penetrate much beyond the inner layers of the myometrium. There is no need for distension of the uterine cavity with flushing media.

Adult↗
PubMed1990

Use of Gaussian beam model in predicting SAR distributions from current sheet applicators.

The Gaussian beam model is shown to be a good predictor of SAR distributions due to current sheet applicators (CSAs). It is fast, efficient and adaptable. SAR distributions from a single applicator and from simple arrays of CSAs in homogeneous and layered lossy media are computed at 434 and 450 MHz at CPU times of less than 60 s. The good agreement between theory and experiment justifies the use of the Gaussian beam model to predict SAR distributions from CSAs.

Computer Simulation↗
PubMed1987

Heat delivery and thermometry in clinical hyperthermia.

This chapter has discussed some recent technical developments and trends in clinical hyperthermia. Several techniques for the treatment of tumours within 3-4 cm of the body surfaces were described. Each technique has its minor advantages and disadvantages; all techniques employing a single applicator produce temperature distributions with considerable gradients. The introduction of microwave and ultrasound techniques using multiple applicators in which there is some control of the pattern of the energy deposition within the treatment area should improve superficial treatments in this respect. A number of electromagnetic devices for regional hyperthermia are being developed and evaluated. The theoretical predictions of their performances are beginning to suggest restrictions to their use; the limited clinical experience is in general agreement with these predictions. Scanned and focussed ultrasound beams may offer the unique possibility of non-invasive, deep, yet localised hyperthermia in some locations. Such systems are at an early stage of their development; if they prove successful, their controlled and safe use will require detailed information of the temperature distributions produced. Invasive methods for inducing hyperthermia can produce relatively good temperature distributions. The development of 'constant temperature seeds' is promising. Both RF and microwave interstitial systems offering individual control of power to several channels should lead to improved temperature distributions. In general, non-invasive thermometry in clinical hyperthermia remains a distant goal, although developments in microwave radiometry may lead to systems with suitable spatial, temporal and temperature resolutions for use in superficial treatments. Invasive thermometry techniques can provide temperature measurements from several points or from along tracks within the treatment volume. The development of computer models to infer temperature distributions from the limited information available will be a major step in quantifying hyperthermal treatments.

Humans↗
PubMed1985

Effect of various regimens of chronic and acute nicotine exposure on myocardial infarct size in the dog.

Smoking is a risk factor for atherosclerotic coronary heart disease, and the risk increases with increasing numbers of cigarettes smoked. The effect of cigarette smoking on the size of acute myocardial infarction (AMI) has not been evaluated. This study describes the effect of 1 component of tobacco smoke, nicotine, on the size of experimentally induced AMI in closed-chest dogs. Daily exposure to nicotine before AMI increased the volume of infarcted tissue (p less than 0.0001). Acute exposure to nicotine (with prior chronic exposure) resulted in a larger volume of infarcted tissue (p less than 0.0001). Thus, chronic, acute and post-AMI exposure to nicotine has an adverse effect on the volume of subsequent infarcted tissue, and continued exposure after AMI further enlarges infarct size.

Animals↗
PubMed1985

Investigation of thermotolerance in mouse testis.

The effect of a two-fraction heat treatment on mouse testis has been assessed by measuring testis weight loss at 1 week after treatment. The rate of repair of 'sublethal' heat damage following the first treatment was dependent on the severity of the treatment. Using a primary treatment of 41.5 degrees C for 30 min, the weight loss following a test treatment of 41.5 degrees C for 30 min returned to that of the test treatment alone within an interval of 16-24 h. Using a milder primary treatment of 40.0 degrees C for 30 min, repair of sublethal heat damage appeared to be complete by 1-2 h. When a single test treatment was used, there was no evidence of heat-induced thermal resistance (thermotolerance) following primary treatments of 40.0 or 41.5 degrees C for 30 min, for periods up to 24 h between treatments. A small degree of thermotolerance could, however, be demonstrated following the most severe primary treatment used if full dose: effect curves were obtained. Thermotolerance, manifest as a decrease in slope, was maximal at approximately 4 h after the primary treatment. The results are discussed with reference to other normal tissue data.

Animals↗