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T V Samulski

Publications and source records attributed to T V Samulski.

At least 55 records · Page 3Linked to original sources
PubMed1987

Heating deep seated eccentrically located tumors with an annular phased array system: a comparative clinical study using two annular array operating configurations.

Regional heating administered with an annular array to 12 patients with deep-seated advanced malignant disease eccentrically located in the lower abdomen and pelvis is compared based on the annular array operating configuration. One configuration (4 quadrants active) delivers radiofrequency power with relative uniformity throughout the patient cross-section. The other (2 quadrants active) allows the radiofrequency power deposition to be shifted preferentially into the eccentrically located treatment volume. Phantom measurements have been made to demonstrate the redistribution of radiofrequency power that results when the annular array is operated in these respective configurations. Systemic responses (i.e. oral temperature rise, changes in blood pressure, and heart rate) to these regional hyperthermia applications are compared and are not significantly different with respect to these heating configurations. Temperature data obtained during treatment sessions using these two annular array operating configurations are analyzed based on the fraction of measured tumor and normal tissue temperatures exceeding or equal to a given index temperature. Although the two quadrant configuration is more efficient in delivering power to the treatment volume, this analysis does not indicate a significant gain in therapeutic heating as a result of this preferential power deposition. Treatment tolerance and heterogeneity with respect to tissue type and blood flow remained the dominant limiting factors with regard to temperatures achieved.

Abdominal Neoplasms↗
PubMed1985

Temperature measurements in high thermal gradients: I. The effects of conduction.

Two temperature probes (a fluoroptic sensor and a metallic thermistor), which are both suitable for stereotaxic implantation, were used in comparative thermometry studies during interstitial microwave heating of the brain in vivo. Thermal distributions having large temperature gradients (5-10 degrees C/cm) were routinely observed. The temperature differentials (delta T) between the 2 probes were position dependent within the thermal field. The maximum difference in temperatures measured, using the 2 probes along identical tracks without a catheter, ranged between 0.5 degree C and 1.8 degree C. Near the brain/air surface, the thermistor measured lower temperatures than the optical probe; however, medial to the antenna, the thermistor temperatures were higher than the optic sensor. The measured temperature discrepancies are the result of smearing due to thermal conduction along the axial length of the metallic thermistor probe. These effects are significantly accentuated when the temperature probes are tracked in catheters. Experiments performed in a nonperfused phantom, heated with the interstitial microwave antenna, demonstrated similar conductive effects. Studies in a nonelectromagnetic environment (flow cell-thermal step gradient) additionally confirmed that thermal conductive artifacts were the major source of temperature error.

Animals↗
PubMed1985

Temperature measurements in high thermal gradients: II. Analysis of conduction effects.

Measurement errors associated with thermal conduction along a temperature probe in regions of high thermal gradients are examined. An analysis of a conducting probe inserted into an insulating catheter for the purpose of temperature mapping gives a means for estimating the effects of thermal smearing on the measured distribution. A comparison is made between the theory and an experimental test case (flow cell-thermal step gradient). Also, an iterative algorithm is developed to correct thermally smeared temperature distributions in order to reconstruct the desired unsmeared distributions. The algorithm is checked for self consistency in the flow cell experiment and is applied to in vivo data obtained during interstitial microwave heating in normal dog brain. Data from flow cell measurements are used to make relative comparisons of the probe conduction artifact for several different temperature probes (2 thermocouple needle probes, a thermistor needle probe and an optical probe) and assorted teflon catheters (16, 18 and 20 ga).

Animals↗
PubMed1984

Direct temperature measurement.

Hyperthermia has little hope of progressing as a clinical modality without accurate assessment of the temperature distributions obtained. At the present time only direct, invasive temperature-measuring techniques are possible, posing severe limitations. Established techniques for clinical temperature measurement have developed over the past few years, and for both ultrasound and electromagnetic hyperthermia it is possible to get temperature-time profiles at a large number of spatial points. Position uncertainty, thermal conduction smearing, and artifactual heating limit the accuracy to about 0.2 degrees (electromagnetic) or 0.5 degrees (ultrasound), but this is probably less of a hindrance than the inadequate percentage of tumor and normal tissue volume for which achieved temperatures can be documented.

Body Temperature↗
PubMed1984

Anatomical site-specific modalities for hyperthermia.

The clinical application of hyperthermia in the treatment of deep-seated tumors remains an empirical science. The pleomorphic nature of the neoplasms and the great diversity in the anatomy and physiology of the individual tumor locations make the treatment of nearly every neoplasm a unique challenge. A wide variety of devices is required, both for the administration of hyperthermia and for the measurement of the temperatures achieved. At Stanford University, these include the BSD Medical Corp. annular phased array system, an isospherical ultrasound device, and interstitial radiofrequency for deep heating. Ultrasound transducers and a variety of microwave applicators are used for superficial hyperthermia. Six illustrative case studies, selected from the 91 patients treated in our program since October 1981, are presented, with discussion and comparison of treatment devices. Difficulties in deep heating were encountered in several instances, believed secondary to the thickness of the s.c. fat, the relatively high heat-induced tumor blood flow, and the presence of adjacent bone. It is suggested that ultimate improvement in clinical results will be possible once a better understanding is achieved of such anatomical and physiological factors.

Adenocarcinoma↗
PubMed1982

Photoluminescent thermometry based on europium-activated calcium sulphide.

A photoluminescent thermometer, based on the transient emission response of a europium-activated calcium sulphide phosphor, is described in detail. This optical thermometry system has special advantages for temperature measurements in microwave and RF fields and potential application in electromagnetically induced clinical hyperthermia. A laboratory system has been constructed which utilises a fibreoptic probe with external diameter 0.8 mm. A system temperature resolution of 0.1 degree C has been achieved in the range 37-47 degrees C.

Calcium↗
PubMedDate not supplied

A phase II trial testing the thermal dose parameter CEM43 degrees T90 as a predictor of response in soft tissue sarcomas treated with pre-operative thermoradiotherapy.

We prospectively evaluated whether delivering a thermal dose of > 10 cumulative equivalent minutes at 43 degrees C to >90% of the tumour sites monitored (CEM43 degrees T90) would produce a pathologic complete response (pCR) in > 75% of high-grade soft tissue sarcomas treated pre-operatively with thermoradiotherapy. The impact of thermal dose on local failure (LF), distant metastasis (DM), and toxicity was also assessed. Thirty-five patients > or = 18 years old with grade 2 or 3 soft tissue sarcomas accessible for invasive thermometry were enrolled on the protocol. All patients received megavoltage external beam radiotherapy (RT) in daily fractions of 1.8-2.0 Gy, five times a week, to a median total dose of 50 Gy and an initial hyperthermia treatment (HT) of I h duration utilizing the BSD 2000 with Sigma 60 or MAPA applicators at frequencies of 60-140 MHz. Further HT was given for patients with CEM43 degrees T90 > 0.5 after initial HT ('heatable' patients), twice a week to a maximum of 10 HT or CEM43 degrees T90 > 100. Of the 35 patients entered, 30 had heatable tumours, one of which was inevaluable for pCR or LF as the patient died of DM prior to surgery, leaving 29 evaluable patients. Of these 29 patients, 15 (52%) had a pCR (95% CI: 37-73%), significantly less than the projected rate of > or = 75% (p = 0.02). Of the 25 heatable tumours that achieved CEM43 degrees T90 > or = 10, 14 (56%) had a pCR (95% CI: 39-78%) significantly less than the projected rate (p = 0.06). Three of the 29 patients (10%) with heatable tumours had a LF, versus 1/5 unheatable tumours (p = 0.48). Fourteen of the 30 patients (47%) with heatable tumours developed DM, versus 2/5 unheatable tumours (p = 1.00). Ten of the 30 patients (33%) with heatable tumours developed treatment-induced toxicity. Thus, no correlation of thermal dose with histologic response was observed. Prospective control of CEM43 degrees T90 failed to achieve the projected pCR rate following pre-operative thermoradiotherapy for high-grade soft tissue sarcomas, despite excellent local control. Possible explanations for this outcome are discussed.

Adult↗
PubMedDate not supplied

3D numerical reconstruction of the hyperthermia induced temperature distribution in human sarcomas using DE-MRI measured tissue perfusion: validation against non-invasive MR temperature measurements.

Essential to the success of optimized thermal treatment during hyperthermia is accurate modelling. Advection of energy due to blood perfusion significantly affects the temperature. Without accurate estimates of the magnitude of the local tissue blood perfusion, accurate estimates of the temperature distribution can not be made. It is shown here that the blood mass flow rate per unit volume of tissue in the Pennes' bio-heat equation can be modelled using a relative perfusion index (RPI) determined with dynamic-enhanced magnetic resonance imaging (DE-MRI). Temperature distributions in two patients treated with hyperthermia at Duke University Medical Center for high-grade leg tissue sarcomas are modelled, and the resultant temperatures are compared to measured temperatures using a non-invasive MR thermometry technique. Significant correlations are found between the DE-MRI perfusion images, the MR temperature images, and the numerical simulation of the temperature field. The correlation between DE-MRI measured values and advective heat loss in tissue is used to scale the perfusion distribution, thereby allowing the continuum model to account for the local thermal impact of vasculature in the tumour. Large vessels in tumour and neighbouring healthy tissue need to be taken into account in order to accurately describe the complete temperature distribution.

Chemotherapy, Cancer, Regional Perfusion↗
PubMedDate not supplied

Variations of focal regions versus numbers and positions of sources in two-dimensional media.

This paper explores the behaviour of the primary and secondary hot spots in homogeneous and two-dimensional inhomogeneous medium. Circular arrays are considered with a radius of up to five wavelengths. The number of sources and their positions in the array are varied, and the influence of these variations on the primary and secondary hot spots is observed. It is found that the primary hot spot reaches its final shape with the addition of a very small number of sources to the array. An increase in the number of sources results in a reduction of the normalized magnitude of the secondary hot spots, but the size of the normalized primary hot spot remains the same. An upper limit of sources in the array exists after which no further reduction of the secondary hot spots is observed. The finite-difference time-domain method (FDTD) is used to obtain the electric-field distribution in the inhomogeneous medium. A genetic algorithm is then applied to find the optimal positions of the antennae in the array.

Algorithms↗
PubMedDate not supplied

A method of MRI-based thermal modelling for a RF phased array.

Magnetic Resonance Imaging (MRI) is an attractive method of temperature monitoring in vivo due to its non-invasive nature. The natural extension of this temperature monitoring is to implement temperature control. This work outlines a method of MRI-based thermal modelling for multi-source phased array heating systems that can potentially be employed, in the future, for real time temperature prediction and control. This method is based on Pennes bioheat equation. It employs the superposition of an empirically acquired basis set of temperature distributions that define the heating system's temperature response. MR thermal images based on the proton resonance frequency shift (PRFS) technique are used to acquire this basis set. The feasibility of this approach is tested in phantom using a radiofrequency (RF) heating system. The results show that this method can accurately reproduce measured temperature distributions outside of the basis set.

Body Temperature↗
PubMedDate not supplied

Ultrasound guided pO2 measurement of breast cancer reoxygenation after neoadjuvant chemotherapy and hyperthermia treatment.

The objective of this study was to determine whether neoadjuvant chemotherapy in combination with hyperthermia (HT) would improve oxygenation in locally advanced breast tumours. The study describes a new optimized ultrasound guided technique of pO2 measurement using Eppendorf polarographic oxygen probes in 18 stage IIB-III breast cancer patients. Prior to treatment, tumour hypoxia (median pO2<10 mmHg) was present in 11/18 patients (average median pO2=3.2 mmHg). Seven patients had well oxygenated tumours (median pO2 of 48.3 mmHg). Eight patients with hypoxic tumours prior to treatment had a significant improvement (p=0.0008) in tumour pO2 after treatment (pO2 increased to 19.2 mmHg). In three patients, tumours remained hypoxic (average median pO2=4.5 mmHg). The advantages of the ultrasound guided pO2 probe are in the accuracy of the Eppendorf electrode placement in tumour tissue, the ability to monitor electrode movement through the tumour tissue during the measurement and the ability to avoid electrode placement near or in large blood vessels by using colour Doppler imaging. The results of this preliminary study suggest that the combination of neoadjuvant chemotherapy and hyperthermia improves oxygenation in locally advanced breast tumours that are initially hypoxic.

Antibiotics, Antineoplastic↗
PubMedDate not supplied

Electromagnetic thermal therapy power optimization for multiple source applicators.

The optimization of power deposition for electromagnetic (EM) thermal therapy is investigated. Several goal or objective functions are examined using a generalized mathematical formulation. These include maximization of: (1) target power absorption, (2) the ratio of target to non-target power absorption, (3) target power absorption weighted by the ratio of target to non-target power absorption, and (4) target power absorption subject to the constraint that the non-target high power volume ('hot spot' volume) is below a chosen level. The merit of these functions was retrospectively tested using an anatomic data base containing 38 cancer patients that were clinically heated with EM phased arrays. CT and/or MRI image data were used to define relevant anatomic geometries and tissue properties for finite element numerical models. Power optimization is achieved by variation of seven available control parameters (four amplitudes and three phases) for these clinical array devices. The results indicate that site dependent improvements in target power absorption can be achieved using these goal functions relative to a configuration that utilizes equal phase and amplitude for the sources. The relative merit among these various functions favours an optimization strategy that maximizes the target power absorption weighted by the ratio of target power to non-target power absorption.

Biophysical Phenomena↗
PubMedDate not supplied

Stanford University institutional report. Phase I evaluation of equipment for hyperthermia treatment of cancer.

From September 16, 1981, through April 4, 1986, a total of 21 radiative electromagnetic (microwave and radiofrequency), ultrasound and interstitial radio-frequency hyperthermia applicators and three types of thermometry systems underwent extensive phantom and clinical testing at Stanford University. A total of 996 treatment sessions involving 268 separate treatment fields in 131 patients was performed. Thermal profiles were obtained in 847 of these treatment sessions by multipoint and/or mapping techniques involving mechanical translation. The ability of these devices to heat superficial, eccentrically located and deep-seated tumours at the major anatomical locations is evaluated and the temperature distributions, acute and subacute toxicities, and chronic complications compared. Average measured tumour temperatures between 42 degrees C and 43 degrees C were obtained with many of the devices used for superficial heating; average tumour temperatures of 39.6 degrees C to 42.1 degrees C were achieved with the three deep-heating devices. When compared to the goal of obtaining minimum tumour temperatures of 43.0 degrees C, all devices performed poorly. Only 14 per cent (118/847) of treatments with measured thermal profiles achieved minimum intratumoural temperatures of 41 degrees C. Fifty-six per cent of all treatments had associated acute toxicity; 14 per cent of all treatments necessitated power reduction resulting in maximum steady-state temperatures of less than 42.5 degrees C. Direct comparisons between two or more devices utilized to treat the same field were made in 67 instances, including 19 treatment fields in which two or more devices were compared at the same treatment session. The analyses from direct comparisons consistently showed that the static spiral and larger area scanning spiral applicators resulted in more favourable temperature distributions. Three fibreoptic thermometry systems (Luxtron single channel, four channel and eight channel multiple [four] probe array), the BSD Bowman thermistor system and a thermocouple system were evaluated with respect to accuracy, stability and artifacts. The clinical reliability, durability, and patient tolerance of the thermometry systems were investigated. The BSD Bowman and third generation Luxtron systems were found clinically useful, with the former meeting all of our established criteria.

Adult↗
PubMedDate not supplied

Heat loss and blood flow during hyperthermia in normal canine brain. I: Empirical study and analysis.

The effects of blood flow and thermal conduction during microwave hyperthermia were investigated in normal canine brain. Heating was accomplished with an external microstrip spiral antenna and temperature measurements were made using a multichannel fluoroptic thermometry system. In order to determine cooling rates, temperature measurements made during cooling were fitted with a model consisting of a constant value and an exponential term. Data from experiments in both perfused and non-perfused brains could be fitted with this simple model. The resulting cooling rates indicated that heat loss by conduction is comparable to that by blood flow. In another series of experiments, temperature measurements were made during several 1 min cooling intervals in which the power was shut off intermittently during a 35 min heating episode. Results were consistent with a 2-3-fold increase in blood flow rate which occurred gradually throughout the course of heating. Parameters that affect the determination of cooling rates are discussed in terms of the bioheat transfer equation. These investigations demonstrate that a simple heat sink model provides a good representation of the cooling data for the thermal distributions obtained.

Animals↗
PubMedDate not supplied

Heat loss and blood flow during hyperthermia in normal canine brain. II: Mathematical model.

A mathematical model for heating and cooling during hyperthermia has been developed from an appropriate solution of a bioheat transfer equation. Predicted cooling rates obtained from the model have been compared with cooling rates obtained from experiments performed on both perfused and non-perfused normal canine brain tissue. The agreement between the predicted and observed cooling rates in non-perfused tissue is satisfactory (within 6-11 per cent) and provides confidence that the conduction process is being accurately represented. The model is then used to estimate the relative contribution of conductive and convective (blood flow) heat loss during cooling for the in vivo experiments. Estimates of blood flow dynamics are made from cooling data taken early and late in a heating course using the model to correct for conductive heat loss. Simplified forms of the bioheat transfer equation are examined. An adequate model for the observed cooling data is one that treats heat loss (both conduction and blood flow) as a heat sink (i.e. an effective perfusion model) rather than an effective thermal conductivity model.

Animals↗