Biomedical subjects

W L Straube

Publications and source records attributed to W L Straube.

13 recordsLinked to original sources

PubMed1995

Simultaneous delivery of electron beam therapy and ultrasound hyperthermia using scanning reflectors: a feasibility study.

PURPOSE: The feasibility of simultaneously delivering external electron beam radiation and superficial hyperthermia using a scanning ultrasound reflector-array system (SURAS) was experimentally investigated and demonstrated. METHODS AND MATERIALS: A new system uses a scanning reflector to distribute the acoustic energy from a planar ultrasound array over the surface of the target volume. External photon/electron beams can be concurrently delivered with hyperthermia by irradiating through the scanning reflectors. That is, this system enables the acoustic waves and the radiation beams to enter the target volume from the same direction. Reflectors were constructed of air-equivalent materials for maximum acoustic reflection and minimum radiation attenuation. Acoustically, the air reflectors were compared to brass reflectors (assumed ideal) for reflectivity and specular quality using several single transducers ranging in frequency from 0.68 to 4.8 MHz. The relative reflectivity was determined from acoustic power measurements using a force-balance technique. The specular quality was assessed by comparing the acoustic pressure fields reflected by air reflectors with those reflected by brass reflectors. Also, acoustic pressure fields generated by a SURAS prototype for two different arrays (2.24 and 4.5 MHz) were measured to investigate field distribution variations as a function of the distance separating the array and the scanning reflector. All pressure fields were measured with a hydrophone in a degassed water tank. Finally, to determine the effect of the air reflectors on electron dose distributions, these were measured using film in a water-equivalent solid phantom after passage of a 20 MeV electron beam through the SURAS. These measurements were performed with the reflector scanning continuously across the electron beam and at rest within the electron beam. RESULTS: The measurements performed using single ultrasound transducers showed that the air reflectors had power reflectivities of 87-96% that of brass, and that for smooth surfaces the reflections from air reflectors were as specular as those from brass reflectors. Acoustic pressure fields measurements of the SURAS for two different arrays showed that the 50% pressure amplitude contours were well-distributed across the projected surface area of the array for different distances separating the array and the reflector. Finally, film dosimetry showed that the electron dose distribution was not affected by the air reflector of the SURAS either for the scanning case or the stationary case. This indicates that the reflectors as made are basically water-equivalent in terms of high energy ionizing radiation. The measured isodoses also indicate that the constructed SURAS prototype would allow the delivery of adequate radiation (90% isodose) to a depth of 2.0 cm. CONCLUSIONS: The results presented show that the SURAS design has the potential to deliver hyperthermia to large superficial tumors, while allowing simultaneous irradiation with 20 MeV electron beams without adverse effects on the radiation dose delivery.

Acoustics↗

PubMed1995

Decrease in culturability of Vibrio cholerae caused by glucose.

The culturability of Vibrio cholerae O1 serotype Inaba strain 569B was decreased by the addition of glucose to cell suspensions in starvation media. A similar effect was observed with sucrose, maltose, and fructose. We term this inhibitory effect glucose shock. It was not observed with arabinose or xylose or with carboxylates, such as acetate and pyruvate. No acidification of the medium occurred in the presence of these carbohydrates. Glucose shock was prevented by the addition of nitrogen or phosphorus sources. In the presence of phosphate, the bacterium produced formic acid from glucose. The phenomenon of glucose shock was also observed in V. cholerae O1 serotype Inaba strain RIMD 2203082 but not in strain RIMD 2203088 (O1 Inaba), IID 936 (O1 Ogawa), or RIMD 2214034 (non-O1). The culturability of Escherichia coli, Enterobacter aerogenes, and Listonella anguillarum did not decrease in starvation media with added glucose. Hence, the phenomenon should have ecological significance in determining the distribution of bacteria in marine ecosystems in situations where carbohydrates are abundant, but nitrogen and phosphorus are limiting.

Glucose↗

PubMed1994

High dose-rate induced temperature artifacts: thermometry considerations for simultaneous interstitial thermoradiotherapy.

PURPOSE: The goal of the present study was to investigate the effect of high dose-rate radiation on a flouroptic thermometry system commonly used during microwave hyperthermia. METHODS AND MATERIALS: Measurements were performed by placing the flouroptic thermometry sensors at distances of < or = 1.5, 5, 10, and 15 mm from a remote afterloading high dose-rate 192Ir source in a water bath (at two different temperatures) and in a tissue equivalent radiation bolus medium. A simulated volumetric clinical setup using a radiation bolus medium was performed with thermometry sensors placed at 1.5, 7.5, 8.4, and 10.6 mm from a scanning high dose-rate source. RESULTS: It was found that high dose-rate radiation caused thermometry artifacts greater than 1.5 degrees C within 2 min for flouroptic thermometers placed 1.5 mm from a 5 Ci activity high dose-rate source. Simple calculations showed that artifacts of this magnitude could not be due to any heating caused by the energy deposited by the high dose-rate source. The artifact decayed, but was still evident 24 h after the exposure. The effect strongly depended on distance with a 0.7 degrees C artifactual increase in temperature seen for the probe 5 mm from the high dose-rate source. Moreover, experiments performed under conditions that represented a clinical setup with a 7 Ci high dose-rate source showed that for exposure times of 10 s, at distances of 1.5 mm, significant artifacts (> 0.5 degrees C) are produced. CONCLUSIONS: These findings indicate that high dose-rate-induced temperature artifacts should be taken into account in the quality assurance procedures for the treatment of patients with simultaneous interstitial thermoradiotherapy.

Artifacts↗

PubMed1994

Theoretical estimation of the temperature dependence of backscattered ultrasonic power for noninvasive thermometry.

The backscattered signal received from an insonified volume of tissue depends on tissue properties, such as attenuation, velocity, density, and backscatter coefficient and on the characteristics of the transducer at the insonified volume. Analysis of scattering in response to a burst of insonification showed that the temperature dependence of backscattered power was dominated by the effect of temperature on the backscatter coefficient. The temperature dependence of attenuation had a small effect on backscattered power. Backscattered power was independent of effects of temperature on velocity. These results were seen in the analysis of two types of inhomogeneity: 1) an aqueous scatterer in a water-based medium and 2) a lipid-based scatterer in the same water-based medium. The temperature dependence of the backscatter coefficient was inferred assuming that the backscatter coefficient was proportional to the scattering cross-section of a small scatterer. Backscattered power increased nearly logarithmically with temperature over the range from 37 degrees to 50 degrees C. Our model predicted a change of 5 dB for the lipid scatterer and a change of up to 3 db for the aqueous-based scatterer over that temperature range. For situations in which temperature dependence of the backscattered power can be calibrated, it may be possible to use the backscattered power level to track temperature distributions in tissue.

Computer Simulation↗

PubMed1990

Enzymatic profiles of 11 barophilic bacteria under in situ conditions: evidence for pressure modulation of phenotype.

Barophilic bacteria are microorganisms that grow preferentially (facultative barophiles) or exclusively (obligate barophiles) under elevated hydrostatic pressure. Barophilic bacteria have been isolated from a variety of deep-sea environments. Attempts to characterize these organisms have been hampered by a lack of appropriate methodologies. A colorimetric method for the detection of 19 constitutively expressed enzymes under in situ conditions of pressure and temperature has been devised, using a simple modification of the commercially available API ZYME enzyme assay kit. By using this method, enzyme profiles of 11 barophilic isolates, including an obligate barophile, were determined. Nine of the 10 facultatively barophilic isolates examined exhibited a change of phenotype in at least one enzyme reaction when tested at 1 atm (1 atm = 101.29 kPa), compared with results obtained under in situ pressure. The assay is simple and rapid and allows for direct determination of enzyme activity under conditions of high pressure and low temperature.

Atmospheric Pressure↗

PubMed1989

Simple, rapid method for direct isolation of nucleic acids from aquatic environments.

Direct isolation of nucleic acids from the environment may be useful in several respects, including the estimation of total biomass, detection of specific organisms and genes, estimations of species diversity, and cloning applications. We have developed a method that facilitates the concentration of microorganisms from aquatic samples and the extraction of their nucleic acids. Natural water samples of 350 to greater than 1,000 ml are concentrated on a single cylindrical filter membrane (type SVGS01015; Millipore Corp., Bedford, Mass.), and cell lysis and proteolysis are carried out within the filter housing. Crude, high-molecular-weight nucleic acid solutions are then drawn off the filter. These solutions can be immediately analyzed, concentrated, or purified, depending on the intended application. The method is simple, rapid, and economical and provides high-molecular-weight chromosomal DNA, plasmid DNA, and speciated RNAs which comigrate with 5S, 16S, and 23S rRNAs. The methods presented here should prove useful in studying both the ecology and the phylogeny of microbes that resist classical culture methods.

Acetates↗

PubMedDate not supplied

Theory and design of "shortened" multiantenna microwave applicators with controllable SAR patterns.

A "shortened" multiantenna hyperthermia applicator has been designed and tested at the Mallinckrodt Institute of Radiology at Washington University School of Medicine. By shortening the distance from antenna to aperture, an applicator is obtained that produces an SAR pattern that is essentially the same as produced by a monopole antenna. By placing several properly spaced probe antennas into the same "shortened" applicator, an applicator is obtained that produces a SAR distribution that is essentially a composite of small overlapping SAR patterns produced by weakly interacting incoherently driven antennas. Such a design significantly improves the applicator's lateral heating efficiency and allows the independent control of temperatures in certain tumor areas by changing the input power to the respective antennas.

Diathermy↗

PubMedDate not supplied

SAR patterns of external 915 MHz microwave applicators.

Analysis of the results from recent clinical trials has shown that tumour size is a significant prognostic factor in eventual tumour control in patients treated with thermoradiotherapy. The critical issue appears to be the adequate coverage of hyperthermia target volume with 'therapeutic temperature'. Therefore one must choose appropriate applicators for the treatment of a given tumour. Accurate knowledge of performance characteristics of the applicators used in clinics thus becomes crucial. In an attempt to take the first step for the appropriate selection of applicators in clinics several commonly used applicators were evaluated according to their 75%, 50%, and 25% two-dimensional SAR (specific absorption rate) contours at depths of 1-3 cm. The data were subsequently approximated by rectangles. This type of information, even with its limitations, is extremely important in implementing quality assurance in hyperthermia. In this communication we will present such information, and the implications in current hyperthermia clinical trials will be discussed.

Biophysical Phenomena↗

PubMedDate not supplied

Potential for localized, adjustable deep heating in soft-tissue environments with a 30-beam ultrasonic hyperthermia system.

Initial heating rates (degrees C/min) along parallel tracks at depths of 1-14 cm in a static, muscle-like phantom were determined from time-temperature profiles obtained with 'Helios', a 30-beam ultrasonic hyperthermia system developed by Varian Associates. Data were taken at a single operating frequency of 556 kHz, for different sets of focal plane ring diameters of the four-ring array applicator, different levels of transducer driving power and two different focal plane depths, 6 cm and 9 cm. In each experiment, at each point of temperature measurement, analysis of temperature versus time data over a 2 min heating interval permitted separation of the desired phantom heating from artefactual heating resulting primarily from absorption of transverse (shear) waves produced at phantom-metal probe catheter interfaces. The results of the studies conducted suggest that in a non-translating carriage mode, Helios can produce axially and laterally localized deep heating in soft tissues for tissue volumes of lateral dimension up to a minimum of 4 cm and tissue depths of at least 11 cm. The results obtained also suggest that Helios can produce laterally localized heating to tissue depths of at least 11 cm without excessive heating of superficial soft-tissue layers, for tissue volumes of lateral dimension up to a minimum of 8 cm. The methodology used in the phantom studies was applied to the production of localized heating in the right lobe of the liver of adult pigs. Temperature versus time profiles obtained in the in vivo studies indicated that, for the set of system parameters employed, concentration of ultrasonic power at greater depths in the liver (e.g. 10.5 cm versus 5 cm) could be achieved, suggesting that Helios should be able to produce localized heating of targeted hepatic volumes when its operating parameters are selected in accordance with effective treatment planning techniques.

Animals↗

PubMedDate not supplied

Dual-antenna applicator for hyperthermia of tumours at intermediate depth.

A dual-antenna applicator with 21 x 26 cm2 aperture, that is fully loaded and operates at 74 MHz, was developed at the Mallinckrodt Institute of Radiology. By placing two antennas into an applicator capable of propagating TE10 mode, a significant enlargement of heating pattern was achieved without an increase in applicator dimensions. When antennas are placed symmetrically about a parallel to the antenna axis of symmetry, the sensitivity of the applicator input impedance to variations of load impedance reduces. Stable coupling of the RF power to the treatment area may be provided. Twenty patients with eccentrically located tumours were treated using this device.

Evaluation Studies as Topic↗

PubMedDate not supplied

Evaluation of the Sigma 60 applicator for regional hyperthermia in terms of scattering parameters.

Scattering parameters adequately describe the interference between ports of a multiportal electromagnetic device when the device dimensions are comparable with the wavelength of the electromagnetic waves within the device. Since the Sigma 60 applicator is a four-port electromagnetic device, the interference between ports (quadrants) is described by a 4 x 4 scattering matrix. The load and frequency dependence of the scattering parameters were studied. The exact values of the parameters depends on the load within the applicator, but typically have minima at frequencies around 80 MHz and sometimes at 100-110 MHz. The effects of the coupling between quadrants can be substantial. Marked changes in the heating pattern can occur, particularly if the phase of the coupling element and the phase between quadrants both approach 90 degrees. Examples are shown in which the effects of coupling can qualitatively alter the intended SAR pattern. Simple steps which can be taken to minimize this phenomenon are demonstrated. Recommendations for clinical practice are discussed. Scattering parameters obtained with a non-absorbing phantom can be used for the quality assurance evaluation of the device.

Biophysical Phenomena↗

PubMedDate not supplied

Clinical system for simultaneous external superficial microwave hyperthermia and cobalt-60 radiation.

A system for simultaneous thermoradiotherapy was devised to investigate the possible benefits and/or complications of thermal radiosensitization in human superficial tumours. The system combines the well-known treatment modalities of external 915 MHz microwave hyperthermia and cobalt-60 teletherapy. Single waveguide applicators are utilized either attached to blocking trays, so that the gamma beam travels through a waveguide and into the patient (en face setup), or in a conventional way with the microwave propagation vector orthogonal to the gamma beam (orthogonal setup). With these setups a radiation fraction can be delivered in the middle of a 60-min, non-interrupted hyperthermia treatment. Temperatures and power level are remotely monitored and recorded outside the Cobalt room. Extensive measurements and testing showed that the operation of the hyperthermia system (generator, applicators, thermometry unit and temperature sensors) was not disrupted by irradiation and that the microwaves were confined to the treatment room and did not interfere with the operation of the Cobalt unit, of an adjacent linear accelerator or of an adjacent radiotherapy simulator. For the en face setup the dose distributions induced in solid water phantoms were uniform with the exception of a narrow (< 0.5 cm) region under the applicators' internal probes where 10-18% reduction exists. This dose defect is clinically smoothed using feathering techniques. The system has been successfully used without technical problems in 51 treatments in 15 patients (18 lesions) in a phase I/II clinical trial. An analysis of the thermal data showed that the temperature distributions achieved during simultaneous delivery have the same general characteristics of those achieved in conventional sequential hyperthermia with microwaves, and that the steady state distributions are maintained during the time of simultaneous irradiation. The tests performed in addition to the preliminary clinical experience clearly indicate that this type of combined therapy is technically feasible and safe. Here the system for simultaneous, external, superficial thermoradiotherapy and the implementation tests performed are described in detail. Preliminary clinical experience and results are also reported.

Cobalt Radioisotopes↗

PubMedDate not supplied

Phase stability of a clinical phased array system for deep regional hyperthermia.

Measurements were performed on the amplifiers of a phased array system to evaluate the dependence of phase on frequency. The power from the amplifiers was terminated into a 50 ohm load at the point of connection to the antennas of the applicator, and the power was sampled to determine the phase relation between amplifier channels. It was found that the measured phase difference between two amplifier channels can: (1) change by as much as 20 degrees with frequency; (2) be as much as 12 degrees different than the prescribed phase; and (3) be as much as 30 degrees different than the phase measured and displayed by the system. Previous studies indicate that in order to accurately plan and deliver treatments with this type of device, it is necessary to know the phase relationship of the array to within at least 20 degrees. Since the differences as great as 20 degrees were obtained under ideal loading conditions, greater differences could result during normal (clinical) loading conditions, and these may not be compensated by the operator because of the inaccurate values reported by the system itself. These findings should be of concern to investigators using these devices since they could result in SAR distributions different from those planned and/or optimized for a particular patient. It is therefore recommended that the measurements such as those reported here also be performed on similar clinical devices as a standard quality assurance procedure so that the power steering capabilities of these systems can be utilized effectively and safely.

Humans↗