Numerical and in vitro evaluation of temperature fluctuations during reflected-scanned planar ultrasound hyperthermia

Temperature fluctuations inside a target volume during reflected-scanned planar ultrasound hyperthermia were investigated numerically and in vitro. The numerical approach consisted of integrating an ultrasonic power deposition model for a scanning ultrasound reflector linear array system (SURLAS) designed for simultaneous thermoradiotherapy, and a three-dimensional transient version of Pennes' bioheat transfer equation. The in vitro approach consisted of delivering hyperthermia to a fixed-perfused canine kidney phantom using a SURLAS prototype. Both approaches allowed the study of temperature fluctuations for several important clinically relevant parameters: scan time, scan distance, perfusion rate and skin cooling. The simulation results showed that the largest temperature fluctuations were located at the opposite ends of the scan window where the scanning reflector comes to a sudden and complete stop and reverses direction. The smallest fluctuations were located at the centre of the scan window. For a given scan distance, the magnitude of the temperature fluctuations increased linearly with increasing scan time, and increased almost linearly as a function of blood perfusion rate. For a scan window of 10 cm x 10 cm and a blood perfusion rate of 5 kg/m3 s, the simulated temperature fluctuations were within +/- 0.5 degree C from the average temperature for scan times less than or equal to 20 s. The in vitro results agreed well with the numerical findings. The measured temperature fluctuations were less than 1.0 degree C for flow rates into the renal artery of less than 200 ml/min and scan times less than 20 s.

DNA damage in rat brain cells after in vivo exposure to 2450 MHz electromagnetic radiation and various methods of euthanasia

The present study was done to confirm the reported observation that low-intensity acute exposure to 2450 MHz radiation causes DNA single-strand breaks (Lai and Singh, Bioelectromagnetics 16, 207-210, 1995). Male Sprague-Dawley rats weighing approximately 250 g were irradiated with 2450 MHz continuous-wave (CW) microwaves for 2 h at a specific absorption rate of 1.2 W/kg in a cylindrical waveguide system (Guy et al., Radio Sci. 14, 63-74, 1979). There was no associated rise in the core body temperature of the rats. After the irradiation or sham treatments, rats were euthanized by either CO2 asphyxia or decapitation by guillotine (eight pairs of animals per euthanasia group). After euthanasia the brains were removed and immediately immersed in cold Ames medium and the cells of the cerebral cortex and the hippocampus were dissociated separately and subjected to the alkaline comet assay. Irrespective of whether the rats were euthanized by CO2 asphyxia or decapitated by guillotine, no significant differences were observed between either the comet length or the normalized comet moment of cells from either the cerebral cortex or the hippocampus of sham-treated rats and those from the irradiated rats. However, the data for the rats asphyxiated with CO2 showed more intrinsic DNA damage and more experiment-to-experiment variation than did the data for rats euthanized by guillotine. Therefore, the guillotine method of euthanasia is the most appropriate in studies relating to DNA damage. Furthermore, we did not confirm the observation that DNA damage is produced in cells of the rat cerebral cortex or the hippocampus after a 2-h exposure to 2450 MHz CW microwaves or at 4 h after the exposure.

Superficial hyperthermia and irradiation for recurrent breast carcinoma of the chest wall: prognostic factors in 196 tumors

PURPOSE

To correlate patient-, tumor-, and treatment-related factors with subsequent local tumor control.

METHODS AND MATERIALS

From 1977 to 1990, 196 subcutaneous/superficial lesions (179 measurable, 17 microscopic) in 151 patients with recurrent breast carcinoma of the chest wall were treated with superficial 915-MHz microwave hyperthermia and irradiation. The definition of min t43 > or = 10 min is that all monitored tumor catheters had a minimum of 1 hyperthermia session with temperatures > 43 degrees C for at least 10 min.

RESULTS

Factors correlating with local control on univariate analysis included length of survival (> or = 1 year vs. < 1 year) (p < 0.0001), specific absorption rate (SAR) (> or = 25% vs. < 25%) (p = 0.0001), minimum t43 > 10 min (p < 0.0001), tumor volume (p < 0.0001), tumor surface area (p < 0.0001), tumor depth (p = 0.0002), number of hyperthermia sessions (p = 0.0003), and current radiation dose (p = 0.0012). On multivariate analysis, the factors best correlated with ultimate local control were SAR (p < 0.001) and number of hyperthermia sessions (p = 0.003).

CONCLUSIONS

Multivariate analysis supports the importance of adequate specific absorption rate (SAR) coverage as a better predictor of local control than tumor volume, surface area, or depth. The explanation is that SAR can be correlated with the tumor surface area and depth, depending on the hyperthermia applicator characteristics. It is recommended that future clinical trials stratify study lesions into either SAR > or = 25% or < 25% because this can be readily estimated prior to initiating treatment. It is also recommended that future clinical trials attempt to have adequate lengths of follow-up after therapy to assess the results in long-term survivors.

Measurement of DNA damage after exposure to 2450 MHz electromagnetic radiation

Recent reports suggest that exposure to 2450 MHz electromagnetic radiation causes DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) in cells of rat brain irradiated in vivo (Lai and Singh, Bioelectromagnetics 16, 207-210, 1995; Int. J. Radiat. Biol. 69, 513-521, 1996). Therefore, we endeavored to determine if exposure of cultured mammalian cells in vitro to 2450 MHz radiation causes DNA damage. The alkaline comet assay (single-cell gel electrophoresis), which is reportedly the most sensitive method to assay DNA damage in individual cells, was used to measure DNA damage after in vitro 2450 MHz irradiation. Exponentially growing U87MG and C3H 10T1/2 cells were exposed to 2450 MHz continuous-wave (CW) radiation in specially designed radial transmission lines (RTLs) that provided relatively uniform microwave exposure. Specific absorption rates (SARs) were calculated to be 0.7 and 1.9 W/kg. Temperatures in the RTLs were measured in real time and were maintained at 37 +/- 0.3 degrees C. Every experiment included sham exposure(s) in an RTL. Cells were irradiated for 2 h, 2 h followed by a 4-h incubation at 37 degrees C in an incubator, 4 h and 24 h. After these treatments samples were subjected to the alkaline comet assay as described by Olive et al. (Exp. Cell Res. 198, 259-267, 1992). Images of comets were digitized and analyzed using a PC-based image analysis system, and the "normalized comet moment" and "comet length" were determined. No significant differences were observed between the test group and the controls after exposure to 2450 MHz CW irradiation. Thus 2450 MHz irradiation does not appear to cause DNA damage in cultured mammalian cells under these exposure conditions as measured by this assay.

Measurement of DNA damage after exposure to electromagnetic radiation in the cellular phone communication frequency band (835.62 and 847.74 MHz)

Mouse C3H 10T1/2 fibroblasts and human glioblastoma U87MG cells were exposed to cellular phone communication frequency radiations to investigate whether such exposure produces DNA damage in in vitro cultures. Two types of frequency modulations were studied: frequency-modulated continuous-wave (FMCW), with a carrier frequency of 835.62 MHz, and code-division multiple-access (CDMA) centered on 847.74 MHz. Exponentially growing (U87MG and C3H 10T1/2 cells) and plateau-phase (C3H 10T1/2 cells) cultures were exposed to either FMCW or CDMA radiation for varying periods up to 24 h in specially designed radial transmission lines (RTLs) that provided relatively uniform exposure with a specific absorption rate (SAR) of 0.6 W/kg. Temperatures in the RTLs were monitored continuously and maintained at 37 +/- 0.3 degrees C. Sham exposure of cultures in an RTL (negative control) and 137Cs gamma-irradiated samples (positive control) were included with every experiment. The alkaline comet assay as described by Olive et al. (Exp. Cell Res. 198, 259-269, 1992) was used to measure DNA damage. No significant differences were observed between the test group exposed to FMCW or CDMA radiation and the sham-treated negative controls. Our results indicate that exposure of cultured mammalian cells to cellular phone communication frequencies under these conditions at an SAR of 0.6 W/kg does not cause DNA damage as measured by the alkaline comet assay.

Acoustic field prediction for a single planar continuous-wave source using an equivalent phased array method

Phased array theory is combined with the Rayleigh-Sommerfeld diffraction integral to predict measured acoustic fields generated by a single-source ultrasonic transducer. The idea is to treat a single-source as a "phased array," which is composed of many small elements. The goal is to find the excitation source for the phased array, that is, the amplitude and phase for each array element, which produces an acoustic field similar to the experimentally measured field generated by the single-source transducer. A pressure field measured at a given plane parallel and close to the face of the transducer in degased water was used to calculate the excitation source of the equivalent phased array using an inverse technique. The excitation source of the equivalent phased array was then used to calculate the acoustic field from this measurement plane to the far field. It was demonstrated that this phased array approach accurately predicted the location of major grating lobes and the general distributions of the near and far pressure fields for four different transducers. This equivalent phased array method (EPAM) used to model a single-source transducer should be useful in both diagnostic and therapeutic ultrasound applications.

An investigation of penetration depth control using parallel opposed ultrasound arrays and a scanning reflector

A theoretical study of penetration depth control in superficial hyperthermia utilizing parallel opposed linear ultrasound arrays and a double-faced (V-shaped) scanning reflector is presented. This is a dual array system (DAS), where one array operates at a low frequency and the other at a high frequency (1 and 5 MHz, respectively in this study). The arrays are positioned facing each other and both are aimed at a double-faced scanning reflector which distributes the energy over the scanned surface. Each reflecting surface is angled at 45 degrees with respect to the sound propagation direction so that both beams are deflected in the same direction toward the treatment volume. The system was designed to be compatible for combined operation with a medical linear accelerator for the delivery of simultaneous thermoradiotherapy. It is demonstrated that by varying the excitation magnitude of one array relative to the other, it is possible to control the magnitude of absorbed energy as a function of depth, and thus improved control of the heating pattern in all three spatial dimensions is obtained. This improvement is demonstrated with bio-heat transfer simulations which show how penetration depth control translates into control of temperature distributions. The simulations also show that the DAS is able to produce more uniform temperature distributions in highly perfused tissue.

An ultrasound system for simultaneous ultrasound hyperthermia and photon beam irradiation

PURPOSE

An existing ultrasound system has been adapted for simultaneous use with external photon beam irradiation. The system is being used to investigate the potential for increased biological benefit of simultaneously combined hyperthermia and external beam irradiation with currently achievable temperature distributions.

METHODS AND MATERIALS

An existing clinical ultrasound system has been modified for simultaneous operation with a 60Co teletherapy machine. The generator, thermometry system, computer, and applicators are located inside the treatment room, while the monitor and system control are located at the control console. Two approaches have been used clinically to combine the two modalities. In the first approach, an en-face setup is used in which the ultrasound beam and the photon beam travel through the same window of entry to the tumor. This is acheived by a reflecting system designed to deflect the ultrasound to the tumor while positioning the ultrasound transducer outside the radiation beam. The reflecting system consists of water and water-equivalent materials except for a 1 mm sheet of polished brass that is used as the reflector. The relative pressure fields were measured in water at the same distance from the ultrasound source using a scanning hydrophone with and without the reflector at the two operating frequencies of the device (1.0 and 3.4 MHz) for two applicators. Radiation dosimetry measurements were performed to determine the relationship between 60Co irradiation through the reflector and absorbed dose. In the second approach the ultrasound and the radiation beam travel into the tumor from different windows of entry such that the radiation beam passes through no portion of the water bolus prior to entering the patient. We have termed this approach the orthogonal approach. For both approaches, the radiation fraction is given in the middle of an uninterrupted 60-min hyperthermia treatment.

RESULTS

The system modifications did not impair the ability to effectively deliver ultrasound hyperthermia or 60Co teletherapy. With the en-face approach the ultrasonic patterns generated with and without the reflector demonstrated that the ultrasound system maintained both a uniform and controllable heating pattern. The 60Co beam had no effect on the performance of the thermocouple thermometers. The radiation beam is attenuated nearly uniformly by the reflector system. To date, 10 patients have been treated with the en-face approach and 12 have been treated with the orthogonal approach (90 treatments).

CONCLUSIONS

The clinical implementation of ultrasound hyperthermia simultaneous with 60Co irradiation is technically and clinically feasible without any complications or hazards to the patient. The implementation of a reflecting device allows en-face delivery of both the ultrasound and 60Co irradiation. Temperatures obtained during simultaneous treatments are comparable to those historically obtained during sequential treatments with the same commercial ultrasound device.

Potential for power deposition conformability using reflected-scanned planar ultrasound

Specialized heating devices for the simultaneous delivery of hyperthermia and ionizing radiation are being developed by several investigators in an effort to increase thermal radiosensitization in clinical treatment. One particular device is the SURLAS (Scanning Ultrasound Refléctor-Linear Array System), which was designed specifically to operate concomitantly with medical linear accelerators. The technical feasibility of the SURLAS has been demonstrated, and a design optimization study has been performed. The main objective of this paper is to demonstrate the potential for power deposition conformability of the SURLAS. This has been done using a thermographic technique which provides qualitative, high spatial-resolution measurements of power deposition distributions. The technique consists of normally insonating one surface of a 1 cm layer of a Polyurethane phantom while the temperature field on the opposite air-exposed surface is recorded using an infrared camera during the first few minutes after power insult. The thermal fields measured in this way are good qualitative estimates of relative power deposition. To demonstrate conformability, a region of 10 cm (the length of the array) by 12 cm (the scanning distance) on the air-exposed phantom surface was divided into 24 sectors (24 subregions with independent power control). Each sector was 2.5 x 2 cm across and long the scanning direction respectively. Several sector insonation patterns were synthesized in an open-loop fashion by properly adjusting power levels to each of the elements of an array as a function of reflector position as the reflector was scanned continuously in a reciprocating fashion at a constant speed. The array was made of a single piezoelectric crystal with resonant frequency of 2.2 MHz and electrically segmented into four 2.5 x 2.5 cm elements. The reflector was made of a 0.5 mm thick Brass plate. Sufficient power was supplied to the array to induce peak temperature elevations of about 10 degrees C in 60s at a scanning speed of 2.4 cm/s. The results show that measured relative power deposition patterns agreed well with programmed insonation patterns demonstrating that the SURLAS possesses great potential for power conformability, and thus, for temperature feedback power deposition control.

Distribution of sewage indicated by Clostridium perfringens at a deep-water disposal site after cessation of sewage disposal

Clostridium perfringens, a marker of domestic sewage contamination, was enumerated in sediment samples obtained from the vicinity of the 106-Mile Site 1 month and 1 year after cessation of sewage disposal at this site. C. perfringens counts in sediments collected at the disposal site and from stations 26 nautical miles (ca. 48 km) and 50 nautical miles (ca. 92 km) to the southwest of the site were, in general, more than 10-fold higher than counts from an uncontaminated reference site. C. perfringens counts at the disposal site were not significantly different between 1992 and 1993, suggesting that sewage sludge had remained in the benthic environment at this site. At stations where C. perfringens counts were elevated (i.e., stations other than the reference station), counts were generally higher in the top 1 cm and decreased down to 5 cm. In some cases, C. perfringens counts in the bottom 4 or 5 cm showed a trend of higher counts in 1993 than in 1992, suggesting bioturbation. We conclude that widespread sludge contamination of the benthic environment has persisted for at least 1 year after cessation of ocean sewage disposal at the 106-Mile Site.

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.

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.

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.

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.

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.

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.

Near-Bottom Pelagic Bacteria at a Deep-Water Sewage Sludge Disposal Site

The epibenthic bacterial community at deep-ocean sewage sludge disposal site DWD-106, located approximately 106 miles (ca. 196 km) off the coast of New Jersey, was assessed for changes associated with the introduction of large amounts of sewage sludge. Mixed cultures and bacterial isolates obtained from water overlying sediment core samples collected at the deep-water (2,500 m) municipal sewage disposal site were tested for the ability to grow under in situ conditions of temperature and pressure. The responses of cultures collected at a DWD-106 station heavily impacted by sewage sludge were compared with those of samples collected from a station at the same depth which was not contaminated by sewage sludge. Significant differences were observed in the ability of mixed bacterial cultures and isolates from the two sites to grow under deep-sea pressure and temperature conditions. The levels of sludge contamination were established by enumerating Clostridium perfringens , a sewage indicator bacterium, in sediment samples from the two sites. The results of hybridization experiments in which DNAs extracted directly from the water overlying sediment core samples were used indicate that the reference site epibenthic community, the disposal site epibenthic community, and the community in a surface sludge plume share many members. Decreased culturability of reference site mixed cultures in the presence of sewage sludge was observed. Thus, the culturable portions of both the autochthonous and allochthonous bacterial communities at the disposal site may be inhibited in situ, the former by sewage sludge and the latter by high pressure and low temperature.

Aperture size to therapeutic volume relation for a multielement ultrasound system: determination of applicator adequacy for superficial hyperthermia

Three-dimensional acoustic and thermal models were developed to simulate superficial hyperthermia treatments using a new multielement planar ultrasonic system. Typical power density and steady-state temperature distributions are presented. A parametric study was performed to determine the relationship between therapeutic volume (volume at and above 42 degrees C) and aperture size (number of active elements). The parameters investigated were: maximum allowable temperature, skin surface temperature, blood perfusion (thermal diffusion length), acoustic absorption, and frequency. Results showed that this device produces well distributed sound beams with lateral dimensions comparable to the aperture size. These simulated results were in agreement with experimental measurements. The simulated temperature distributions were uniform at each depth across the applicator's aperture. The main heating characteristics found were: (1) the therapeutic volume was directly proportional to the aperture size; (2) the lateral dimensions of the therapeutic volume were independent of the parameters studied and remained practically constant with depth for several centimeters, with a very rapid increase near the skin surface and a very rapid fall off at depth; and (3) therapeutic penetration was strongly dependent on maximum allowable temperature, frequency, and acoustic absorption; and weakly dependent on blood perfusion and skin surface temperature. These heating characteristics are new in commercial systems for superficial hyperthermia. Despite the well-distributed beams, it was found that in order to produce adequate hyperthermia with this device the lateral dimensions of tumors must be smaller than the applicator's active aperture and that thermal depth coverage must be monitored during treatments. Guidelines for aperture selection and thermometry strategies are discussed.

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.

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.

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.

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.

Particulate DNA in Smoker Fluids: Evidence for Existence of Microbial Populations in Hot Hydrothermal Systems

As part of an interdisciplinary study of hydrothermal vents on the Endeavour Segment of the Juan de Fuca Ridge, we used the submersible ALVIN to collect 57 fluid samples in titanium syringes and Go Flo Niskin bottles from 17 different hot vents (smokers and flanges) and their environs for the purpose of extracting particulate DNA. The relative purity of the vent fluids collected was determined by Mg content as an indicator of seawater entrainment. Particulate material concentrated from these samples was lysed enzymatically (enz) and by a combination of enzyme and French press treatment (fp). Concentrations of partially purified DNA recovered from these lysates were determined spectrofluorometrically by using the dye Hoechst 33258. Ambient seawater surrounding the vents was found to contain low DNA concentrations, 0.18 to 0.32 ng of DNA per ml ( n = 4; mean enz = 0.23 ± 0.05; mean fp = 0.26 ± 0.05), while low-temperature vent samples yielded significantly higher concentrations of 0.37 to 2.12 ng of DNA per ml ( n = 4; mean enz = 0.97 ± 0.68; mean fp = 1.05 ± 0.54). Although DNA recovery values from superheated (210 to 345°C) flange samples (mean enz = 0.14 ± 0.10; mean fp = 0.12 ± 0.14) were not significantly different from ambient seawater values, most of the superheated (174 to 357°C) smoker fluid samples contained particulate DNA in concentrations too high to be attributable to entrained seawater. Detailed sampling at one smoker site demonstrated not only the existence of significant levels of particulate DNA in the superheated smoker fluids but also the presence of an elevated microbial population in the buoyant plume 20 to 100 m above the smoker. These results underscore the heterogeneity of smoker environments within a given hydrothermal vent field and indicate that microorganisms exist in some superheated fluids.

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.

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.

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.