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Biomedical subjects

F A Gibbs

Publications and source records attributed to F A Gibbs.

At least 55 records · Page 3Linked to original sources
PubMed1984

Regional hyperthermia: a clinical appraisal of noninvasive deep-heating methods.

The concentric single-turn self-resonant coil operated at 13.56 MHz (CC) and the annular array applicator (AA) operated at 55 to 100 MHz are the only regional heating devices the clinical use of which has been subjected to sufficient thermometric characterization to be evaluable. The clinical heating characteristics and toxicity of both devices are reviewed. When spatial temperature measurements have been made during clinical treatments with the CC, the observed temperatures have been consistent with theoretical predictions and phantom studies; temperatures fall with increasing radial depth, and potentially injurious heating in superficial normal tissues and ineffective heating in deep-seated tumor loci have been commonly observed. The CC is ineffective in heating central pelvic tumors due to inadequate penetration and power-limiting sacrococcygeal pain. The AA has been demonstrated to heat many deep pelvic tumors to maximum temperatures greater than 42-43 degrees without significant side effects, but further study is needed to determine the feasibility of achieving higher minimum tumor temperatures and longer treatment durations. In the upper abdomen, the AA appears to have a slight superiority in rapid tumor heating at depth, but both devices have major limitations with insufficient penetration (CC) or treatment limiting systemic heating (AA). There has been no adequately thermometrically documented experience with heating in the deep thorax with either device.

Abdominal Neoplasms↗
PubMed1983

Change in the in vivo hyperthermic response resulting from the metabolic effects of temporary vascular occlusion.

Previous workers have reported that clamping of animal tumors in vivo enhanced the effect of hyperthermia; the enhancement has been attributed to pH and nutritional effects of vascular occlusion. It has not been clear, however, the degree to which improved heating patterns or effects on the tumor cells and vasculature from the clamping procedure itself might have contributed to the observed effect. In the experiments herein reported, care was taken to insure comparable heating of C3H mouse mammary tumors transplanted on the flank whether clamped or unclamped. Clamping for one hour with hyperthermia during the final 30 minutes caused a marked thermosensitization as measured by tumor control. The temperature at 30 minutes heating to control 50% of the tumors for 120 days (TCT 50-120) was reduced from 46.8 degrees C in controls to 43.5 degrees C in clamped tumors, a difference of 3.3 +/- 0.09 degrees C. No cytotoxicity from the clamping alone was evident by assessment of subsequent tumor growth and no lasting vascular effects could be detected by 133Xe washout and tumor growth. Since the techniques used produced essentially identical heating patterns, we conclude that the striking enhancement in hyperthermic response in clamped tumors can be attributed to the metabolic consequences of temporary vascular occlusion.

Animals↗
PubMed1983

"Thermal mapping" in experimental cancer treatment with hyperthermia: description and use of a semi-automatic system.

The regions of tumor which are least adequately heated during experimental hyperthermia treatments will most likely determine the ultimate probability of tumor control. Temperature inhomogeneity during local or regional hyperthermia is often marked, and stationary temperature probes yield very little information about the adequacy or inadequacy of tumor heating. Fine catheters can be placed through the tumor bearing region and temperatures recorded at various points within these catheters, thus yielding valuable data about temperature variations within the volume of interest. The "thermal mapping system" (TMS) described herein provides a method for remotely sampling these temperature variations in a semi-automatic manner in several catheters simultaneously. Its application in conjunction with a commercial hyperthermia system is described and clinical examples of its use and importance are provided.

Carcinoma, Squamous Cell↗
PubMed1983

Capillary blood flow in murine tumors, feet, and intestines during localized hyperthermia.

Changes in capillary blood flow were determined by serial measurements of xenon-133 (133Xe) washout rates from "Slow-line" C3H-mouse mammary carcinomas transplanted onto the flank or hindfoot, from non-tumor-bearing hindfeet, and from the lumen of a short portion of the proximal jejunum. The core temperature of the pentobarbital-anesthetized mice was externally controlled. Special techniques allowed selective rapid and uniform heating by water bath immersion of even the flank tumors and nonexteriorized jejunum. Immersion in a 44 degrees C bath immediately doubled washout rates not only from the immersed tumor, but also from a contralateral tumor that was not heated. This result and behavioral observations were consistent with an arousal-induced increase in cardiac output to the tumors that increased the capillary blood flow in them. In contrast, washout rates from the hindfeet or intestinal lumen did not increase unless the foot or intestine in question was itself heated, which is consistent with normal tissues having intrinsic mechanisms for regulating their own capillary blood flow that the Slow-line tumor lacks. This lack could complicate the design and interpretation of hyperthermia experiments in vivo. Immersion of Slow-line tumors in a 44 degrees C bath for 20 min did no microvascular damage detectable from 133Xe washout rates during the heating or for 1 hr subsequently. Washout rates from both foot and flank tumors had dropped by one-half after 41-43 min in the 44 degrees C bath. Equivalent declines had occurred after 60 min for the intestine and 100 min for the hindfeet.

Adenocarcinoma↗
PubMed1982

Heating patterns induced by a 13.56 MHz radiofrequency generator in large phantoms and pig abdomen and thorax.

Heating patterns generated by a commercially available 13.5 MHz radiofrequency generator and induction coil hyperthermia system in human size phantoms and a 230 pound pig were studied using a multichannel computer-monitored thermometry system that is noninteractive in electromagnetic fields. The phantom studies were composed of synthetic muscle equivalent material and fresh tissue. The pig was heated in the regions of the upper abdomen and the midthorax, both under anesthesia and dead. The temperature was measured along fine penetrating catheters at 1 cm intervals in all experiments. In a homogeneous cylindrical phantom, under our measurement conditions, the temperature profile across the diameter is parabolic with marked superficial heating and essentially no central heating. In nonhomogeneous phantoms and in the pig, the symmetry of this profile was distorted but the basic pattern of marked superficial heating and nearly absent deep central heating remained. Blood flow in the living animal produced some thermal smoothing. It is considered probable that substantial radial temperature gradients will exist within eccentrically located human tumors heated with this device and that certain deep central tumors will be difficult or impossible to heat. Determination of its ultimate value for investigational; clinical hyperthermia studies will require accurate temperature mapping of tumors and normal tissues in various anatomic sites in comparison with other approaches to deep heating.

Abdomen↗
PubMed1982

How to read EEGs.

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Computers↗
PubMed1981

Clinical evaluation of a microwave/radiofrequency system (BSD Corporation) for induction of local and regional hyperthermia.

The technical aspects of an experience with clinical hyperthermia utilizing the BSD-1000 and BDS annular phased array applicator are reviewed. The design and operation of the basic console functions of the BSD apparatus relating to temperature data presentation and recording and computer control leave little need for significant improvement. Such improvements as may eventually be desired can probably be made as software changes in the computer programs. The 100 W generator capacity is occasionally inadequate to drive even a single applicator and certainly inadequate to supply multiple applicator arrays or larger low frequency applicators. Amplifiers will eventually be added for the frequency ranges of greatest interest. The temperature probes and utilization routines have been excellent but their diameter is undesirably large. However, the design of the basic instrument is such that improved smaller probes and systems for dynamic temperature sampling matrices can be interfaced readily. Due to the limited superficial volumes that can be presently heated with this device, most important potentially curable tumors cannot be treated. Possible important exceptions to this are a number of sites in the upper respiratory tract. The depth and superficial extent of heatable volumes may be moderately extended with increased power, appropriate study of applicator arrays and new applicator designs. Provisions for surface temperature control are important and will need to be incorporated. The annular phased array applicator, though still a prototype design, has demonstrated encouraging results regarding its possible use for regional heating of central abdominal and thoracic tumors. Improvements in "human engineering" and study of the effects and implications of departures from basic cylindrical anatomy are required and are in progress. The improved sophistication in temperature sampling techniques described is considered important for adequate monitoring of temperature gradients in the abdomen and chest.

Computers↗
PubMed1981

[Electroencephalogram in congenital anophthalmia (author's transl)].

Dysgenesis of the eye produces occipital needle sharp spikes. Neither the age and maturational state of the eye nor the brain create the pathophysiologic conditions which give rise to needle sharp spikes. It seems rather that deafferentation of the visual cortex gives rise to an increase in its irritability which make it fire off in this special manner. Cannon and Rosenblueth presented evidence that, as a general rule, deafferented systems tend to become hyperexcitable.

Adolescent↗
PubMed1980

Direct sagittal computed tomographic scans in the radiographic evaluation of the pelvis.

The authors describe a method for obtaining direct sagittal and coronal computed tomographic (CT) scans of the pelvis using a special accessory table adapted for use in wide-aperture whole-body scanners. In these scans the spatial and density resolution are nearly equivalent to those in axial scans. A case is described in which sagittal scanning helped define a pelvic mass.

Adult↗
PubMed1976

The metal/tissue interface effect in irradiation of the oral cavity.

Metal dental prostheses or overlays may lead to increased mucosal reactions of adjacent tissue surfaces during intensive irradiation of the oral cavity. The dosimetry of this phenomenon was investigated by irradiating dental phantoms with 4-and 6-MeV photons. Gold and amalgam interfaces may produce local mucosal doses as high as 150-170% depending on the beam geometry, but doses of 111-126% for gold crowns and about 109-118% for amalgam fillings were found for opposed-beam configurations. 2-4 mm of tissue-equivalent absorber is sufficient to re-establish a homogeneous dose distribution and should be employed throughout therapy whenever dental extraction is unwarranted. The radiobiological exaggeration of the interface effect in treatment with opposed beams using one field per day is discussed.

Absorptiometry, Photon↗