Tumor bed brachytherapy with a mesh template: an accessible alternative to intraoperative radiotherapy.

BACKGROUND AND OBJECTIVES: Locally advanced and recurrent malignancies often require adjuvant radiotherapy to achieve tumor control. We report our experience with a technique that uses an intraoperatively placed mesh template for the delivery of radiotherapy. METHODS: from 1988 to 1996, 14 patients were treated with tumor bed brachytherapy using this mesh technique. Sites of involvement included the head and neck region (n = 6), abdomen/pelvis (n = 4), retroperitoneum (n = 3), and the lower extremity (n = 1). During surgery, plastic catheters were evenly placed within a mesh template (Vicryl or Marlex), which was positioned in the tumor bed. The catheters were afterloaded with radioactive sources once the final pathology had been determined and the patient required limited nursing care. Radiation dose was titrated to the surgico-pathologic findings (e.g., margin status). RESULTS: All of the patients tolerated the procedure without experiencing acute or chronic sequelae. The median survival time was 13 months. Local control was achieved in 11 of 13 evaluable patients, with an actuarial local control of 82% at 6 months. CONCLUSION: Tumor bed brachytherapy with a mesh implant is a practical technique to improve tumor control and warrants further investigation.

Mapping of human local pulmonary ventilation by xenon enhanced computed tomography.

Functional maps of local pulmonary ventilation are derived from serial computed tomographic images acquired prior to and during a short period of inhalation of subanesthetic xenon/oxygen gas mixtures. Preliminary results from human studies yield quantitative maps of local ventilation rates with excellent anatomic specificity demonstrating nonuniformities in the distribution of ventilation in normal and abnormal human lungs.

Diode array digital radiography: initial clinical experience.

Initial clinical results are described for a new method of digital radiography based on high-detail self-scanning linear diode arrays which overcome many of the limitations of present film or other digital methods. The technique uses a fan-shaped x-ray beam to produce a nearly scatter-free image on a phosphor strip that is fiber-optically coupled to six self-scanning arrays of light-sensitive diodes spaced 0.025 mm, thus providing 6,144 discrete sensors across the field of view. Because these diodes have a greatly expanded dynamic range and operate at very low noise, it becomes possible to visualize small density differences or contrast below 1% both in the light and dark areas of the image. Because of the efficiency of detection and display, radiation doses can be reduced for a given information content. Our preliminary clinical studies have shown to broad application of our method in examining the chest and abdomen and in performing intravenous digital arteriography.

Progress in cerebrovascular disease: local cerebral blood flow by xenon enhanced CT.

A noninvasive technique for measuring local cerebral blood flow (LCBF) by xenon enhanced x-ray transmission computed tomography (CT) has been developed an reported quite extensively in recent years. In this method, nonradioactive xenon gas in inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computed tomography. Time dependent xenon concentrations within various tissue segments in the brain are used to derive both local partition coefficient (lambda) and LCBF. An assessment of this method reveals that although it provides functional mapping of blood flow with excellent anatomic specificity, there are distinct limitations. The assumptions underlying this methodology are examined and problems associated with various potential applications of this technique are discussed.

Errors associated with single-scan determinations of regional cerebral blood flow by xenon enhanced CT.

Possible errors in the determination of xenon concentrations in arterial blood, and uncertainties in CT tissue enhancements during inhalation of xenon-oxygen mixtures, are used to assess errors in the determination of regional cerebral blood flow by the in vivo autoradiographic (single-scan) technique. The results of this study indicate that errors associated with the determination of xenon concentrations in arterial blood decrease rapidly as the time of scanning after the initiation of xenon inhalation is increased. Analysis of errors caused by statistical uncertainties in image enhancement indicate that time of scanning is optimal between 1.5 and 2.5 min for determination of fast flow, while errors in slow-flow determinations gradually decrease as the time of scanning increases.

In vivo mapping of local cerebral blood flow by xenon-enhanced computed tomography.

A noninvasive technique has been developed to measure and display local cerebral blood flow (LCBF) in vivo. In this procedure, nonradioactive xenon gas is inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computerized tomography. The time-dependent xenon concentrations in various anatomical units in the brain are used to derive both the local partition coefficient and the LCBF. Functional mapping of blood flow with excellent anatomical specificity has been obtained in the baboon brain. The response of LCBF to stimuli such as changes in carbon dioxide concentrations as well as the variability in LCBF in normal and diseased tissue can be easily demonstrated. This method is applicable to the study of human physiology and pathologic blood flow alterations.

Regional pulmonary ventilation measurements by xenon enhanced dynamic computed tomography: an update.

New developments in computed tomographic technology permit rapid, serial images that may yield information concerning tracer kinetics through a large tissue volume. One possible application of these developments is the derivation of local lung ventilation by observing the temporal changes of stable xenon concentrations. Preliminary results from six multilevel ventilation studies in dogs demonstrate that the lung may be repeatedly imaged during reproducible phases of respiration even when interscan table incrementation is employed to survey a number of tissue segments and breathing is permitted between scans. In addition, subanesthetic xenon concentrations provide adequate enhancement for possible quantification.

Xenon and iodine enhanced cerebral CT: A closer look.

Xenon and iodine enhanced dynamic computerized tomography (CT) have been used experimentally to obtain both qualitative and quantitative information on local cerebral blood flow in both normal and infarcted tissue. Direct comparisons between Xenon enhancement, iodine enhancement and pathological findings demonstrate significant differences between results derived from each of the 2 in vivo techniques. While iodine enhanced dynamic CT yields valuable information concerning the patency and density of vasculature, xenon enhanced studies can provide highly focal information on cerebral tissue perfusion.

Side effects of xenon inhalation.

Short- and long-term side effects during and after inhalation of premixed xenon oxygen (28-47%) from 12 studies are reported. While all but one subject tolerated xenon inhalation without ill effects, that individual did experience unpleasantly severe dysesthesias and a brief period of unresponsiveness. We believe that further human studies with xenon inhalation should be conducted to explore possible early indicators for reduced tolerance of xenon by certain individuals.