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Biomedical subjects

K A Weaver

Publications and source records attributed to K A Weaver.

At least 37 records · Page 2Linked to original sources
PubMed1991

Pretreatment of formula with sodium polystyrene sulfonate to reduce dietary potassium intake.

Sodium polystyrene sulfonate (SPSS) is commonly administered for the acute and chronic treatment of hyperkalemia. Its oral intake is complicated by poor compliance due to multifaceted reasons. We therefore analyzed a method of reducing potassium (K) in formula by pretreatment with SPSS. If effective, this would bypass complications of enterally administered SPSS and provide low-K formula. Thirteen formulas and nutritional supplements were pretreated with SPSS to determine if one could bind K and provide formulas with decreased K contents. Using an SPSS concentration of 1 g/l mEq K in the formula, 62 +/- 2.6% (P less than 0.01, mean +/- SEM) of the K was removed in 30 min, while the sodium (Na) concentration was increased by 234 +/- 37% (P less than 0.01). Analysis suggests that the disproportionate increase in Na is due to exchange for calcium (Ca) and magnesium (Mg), interaction with proteins, and Na suspended with SPSS in the formula. Thus, SPSS pretreatment of formula is an effective method of making low-K formula, but the increase in Na exceeds the K reduction. Attention to possible complications of increased Na intake as well as decreased Ca and Mg intake is warranted.

Humans↗
PubMed1991

External irradiation followed by an interstitial high activity iodine-125 implant "boost" in the initial treatment of malignant gliomas: NCOG study 6G-82-2.

Between January 1982 and January 1990, 107 patients with unifocal, circumscribed malignant gliomas participated in a non-randomized trial testing brachytherapy in their initial treatment. Focal external irradiation (6000 cGy) was combined with an implant of high-activity iodine-125 (5000-6000 cGy) and six courses of procarbazine, lomustine, and vincristine. Of the 101 evaluable patients, 63 received implants. Of these, 29 had non-glioblastoma anaplastic gliomas, and 34 had glioblastoma multiforme. The other 38 did not receive implants, in most cases because radiation therapy failed to reduce the size of the tumor. The median survival was 165 weeks for all evaluable patients with non-glioblastoma anaplastic gliomas, 157 weeks for those with implants, 67 weeks for all evaluable glioblastoma patients, and 88 weeks for those with implants. Of the glioblastoma patients with implants, nine were alive after 2 years, and three were alive after 3 years. In each of the groups, nearly half the patients underwent reoperation for clinical deterioration, increasing steroid dependency, and increasing mass effect at the implantation site after 46.1 weeks (median) for glioblastoma multiforme and 41.3 weeks for non-glioblastoma patients. Karnofsky Performance Scores showed only a small decline in performance after brachytherapy. Patients receiving implants for non-glioblastoma anaplastic gliomas had a mean Karnofsky Performance Score of 91% (range 90-100%) after 1 month and 78% (range 60-100%) 30 months after brachytherapy. Those treated for glioblastoma multiforme had a mean Karnofsky Performance Score of 86% (range 60-100%) at 1 month and 75% (range 60-100%) at 24 months. The quality of life of treated patients appears to be satisfactory. On the basis of comparisons with previous studies, we conclude that a brachytherapy "boost" after external irradiation may be valuable for some patients with glioblastoma multiforme but not for those with non-glioblastoma anaplastic gliomas.

Adult↗
PubMed1991

Interstitial irradiation and hyperthermia for the treatment of recurrent malignant brain tumors.

Between June 1987 and June 1989, 29 recurrent malignant gliomas or recurrent solitary brain metastases in 28 patients were treated in a Phase I study of interstitial irradiation and hyperthermia. Patient age ranged from 18 to 65 years, and the Karnofsky Performance Status scores ranged from 40 to 90%. There were 13 glioblastomas, 10 anaplastic astrocytomas, 3 melanomas, and 3 adenocarcinomas. Catheters were implanted stereotactically after computed tomography-based preplanning. Hyperthermia was administered before and after brachytherapy, using one to six 2450- or 915-MHz helical coil microwave antennas and one to three multisensor fiberoptic thermometry probes. The goal was to heat as much of the tumor as possible to 42.5 degrees C for 30 minutes. Within 30 minutes after the first hyperthermia treatment, implant catheters were afterloaded with high-activity iodine-125 seeds delivering tumor doses of 32.6 to 61.0 Gy. Most patients had no sensation of heating. Complications included seizures in 5 patients, reversible neurological changes in 9 patients, a scalp burn in 1, and infections in 3. Of 28 evaluable 2-month follow-up scans, 11 showed definite improvement in the radiological appearance of the tumor, 4 were slightly improved, 7 were stable, and 6 showed tumor progression. Ten patients underwent reoperation for persistent tumor and/or necrosis. Eleven of 28 patients are alive 40 to 97 weeks after treatment. Thirteen patients died of a brain tumor, 2 died of extracranial melanoma metastases, 1 died of new brain melanoma metastases, and 1 died of a pulmonary embolus. The median survival was 55 weeks overall. Median survival has not yet been reached for the anaplastic astrocytoma subgroup. We conclude that interstitial brain hyperthermia using helical coil microwave antennas is technically feasible. The level of toxicity is acceptable, and the computed tomographic response rate is encouraging.

Adenocarcinoma↗
PubMed1991

Relationships between scores on Wechsler Preschool and Primary Scale of Intelligence--Revised and Stanford-Binet IV.

The Wechsler Preschool and Primary Scale of Intelligence--Revised and the Stanford Binet-Intelligence Scale: Fourth Edition were given to 51 preschool, kindergarten, first, and second grade students. Twelve of 15 Pearson correlations between Wechsler IQs and composite and area scores of the Stanford-Binet IV were statistically significant. It is apparent that the two tests measure similar, but not identical, concepts.

Child↗
PubMed1989

Combined total body X-ray irradiation and total skin electron beam radiotherapy with an improved technique for mycosis fungoides.

Twelve consecutive patients with advanced stage mycosis fungoides (MF) were treated with combined total body X ray irradiation (TBI) and total skin electron beam radiotherapy (EBRT). Six had generalized plaque disease and dermatopathic nodes, three had tumor stage disease and node biopsy positive for mycosis fungoides, and three had erythroderma/Sezary syndrome. The treatment regimen consisted of split course total body X ray irradiation, given in twice weekly 15 cGy fractions to 75 cGy, then total skin electron beam radiation therapy given in once weekly 400 cGy fractions to a total dose of 2400 cGy. Underdosed areas and areas of greatest initial involvement were boosted 400 cGy twice weekly for an additional 1200 cGy. This was followed by a second course of total body X ray irradiation, to a total dose of 150 cGy. The total skin electron beam radiotherapy technique is a modification of an established six position EBRT technique for mycosis fungoides. Measurements to characterize the beam with and without a lexan scattering plate, demonstrated that the combination of no-plate beams produced better dose uniformity with a much higher dose rate. This improved technique is particularly advantageous for elderly and/or frail patients. Nine (75%) of the 12 patients achieved complete response (CR). The other three had significant improvement with greater than 80% clearing of their disease and resolution of symptoms. All six patients with generalized plaque disease achieved complete response and remained free of disease from 2 to 16 months. Two of three node positive patients also achieved complete response; one, with massive biopsy-documented mycosis fungoides nodal disease and deep open tumors, remained relapse-free over 2 years. Only one of the three patients with erythroderma/Sezary syndrome achieved a complete response, which was short lived. Therapy was well tolerated. No significant hematological toxicity occurred. Although total body X ray irradiation and total skin electron beam radiotherapy produced excellent palliation of patients with advanced stage mycosis fungoides, new strategies to provide more effective systemic treatment are needed.

Adult↗
PubMed1989

Survival and quality of life after interstitial implantation of removable high-activity iodine-125 sources for the treatment of patients with recurrent malignant gliomas.

Between January 1980 and January 1988, 95 evaluable patients with recurrent, unifocal, supratentorial malignant gliomas were reirradiated with high-activity iodine-125 sources implanted directly into tumor in afterloaded, removable catheters using computerized tomography-directed stereotaxy. A tumor dose of 5270-15,000 cGy was delivered at a maximum distance of 0.5 cm from the rim of the contrast-enhancing mass seen on CT scans. The median survival for the 50 patients with anaplastic astrocytoma was 81 weeks and for 45 patients with glioblastoma multiforme it was 54 weeks. The 18- and 36-month survival rates for patients with anaplastic astrocytoma were 46% and 28%, respectively; the 18- and 36-month survival rates for patients with glioblastoma multiforme were 22% and 8%, respectively. Because of clinical deterioration, increasing steroid dependency, and increasing mass effect at the implantation site seen on CT scans, necrotic tissue was excised from 47 patients (49%) at craniotomy; in some patients, tumor was mixed with necrotic tissue. The survival of reoperated patients was significantly longer compared with patients who did not undergo this procedure. Serial determination of the Karnofsky Performance Score (KPS) showed that there was no significant deterioration for the group as a whole during the 6 months immediately after implantation. At 18 months, 33 of the patients were alive; KPS ranged between 50 to 90 (mean 79) and 67% were steroid dependent. At 36 months, 18 patients were alive; 17 patients were evaluable with KPS that ranged between 40 to 90 (mean 76) and 53% were steroid dependent. Eleven of the 17 evaluable long-term survivors had a KPS of 80 or higher with a mean of 87. Interstitial brachytherapy may provide long-term survival in selected patients with recurrent malignant gliomas who have been irradiated previously with conventional teletherapy. The quality of life in the majority of long-term survivors appears to be quite satisfactory. Further attempts to control tumor growth using this modality appear to be warranted.

Adolescent↗
PubMed1987

Brachytherapy of recurrent tumors of the skull base and spine with iodine-125 sources.

Thirteen patients with recurrent, previously irradiated tumors of the skull base or spine were reirradiated with 125I sources implanted interstitially using microsurgical or stereotactic techniques. Patients harbored difficult, end-stage recurrences of chordoma, meningioma, malignant meningioma, fibrosarcoma, invasive pituitary adenoma, and malignant schwannoma. In two other patients with malignant meningioma, the dose of external radiation was augmented by implanting 125I sources during the initial operation for excision of the lesion or at a separate surgical procedure after conventional teletherapy. Microsurgical implantation of 125I sources into basal tumors was limited by the difficulties inherent in operating in this region; it is not possible to visualize the entire tumor that requires implantation. Three of five chordomas stabilized or regressed; these patients probably benefited from the procedure. Two patients with recurrent malignant meningiomas had long term remission after interstitial brachytherapy. Interstitial 125I brachytherapy for recurrent tumors at the base of skull or adjacent to the spine can be more successful only if more aggressive surgical exposures of these regions are attempted. Implantation of sources for a "boost" dose, either microsurgically during the initial surgical resection of the lesion before conventional teletherapy or stereotactically after conventional teletherapy, may be a valuable adjunct to external irradiation for the control of potentially devastating tumors (such as chordomas and malignant meningiomas) before they recur with the severe consequences seen in the patients reported here.

Adenoma↗
PubMed1986

Normal brain iodine-125 radiation damage: effect of dose and irradiated volume in a canine model.

High-activity iodine-125 sources in plastic catheters were surgically placed in the cerebral white matter of healthy beagle dogs and later removed. Reference doses, calculated at a point 0.75 mm from the source, ranged from 10 to 40 Gy. Necrosis, vascular-related damage, and edema were quantified by computed tomography. Volumetric analyses were used to derive the relationship of dose and dose rate to necrosis and contrast enhancement. The extent of necrosis was related to irradiated volume; a minimum effective dose averaging 180-200 Gy was required to induce this type of damage. Contrast enhancement was less dependent on irradiated volume or total dose. The extent of radiation-induced edema was directly related to the volumes of necrosis plus contrast enhancement. Noninvasive serial studies in a well-characterized in vivo model can address specific clinically related questions on damage to normal tissue after interstitial irradiation.

Animals↗
PubMed1985

The hearing aid feedback path: mathematical simulations and experimental verification.

Acoustic feedback in hearing aids has received little attention in the literature. Feedback occurs when stability conditions of the open-loop transfer function of an in situ hearing aid are violated. Solving the feedback problem will first require knowledge of the open-loop transfer function. Included in the open-loop transfer function is the acoustical path by which sound emanating from the earmold vent returns to the microphone (i.e., the feedback path). Reported herein are two different mathematical procedures for simulating transfer functions of the feedback path of an eyeglass-type hearing aid. In one procedure the vent exit was modeled as a point source of sound located on a flat plane, while it was treated as a point source on a sphere in the other. Results of laboratory experiments indicate that the mathematical models accurately predict those acoustic phenomena for which they were intended: point sources on plane and spherical baffles. Results of manikin experiments showed both models to be less accurate for simulating the feedback path around the human head. The maximum difference between experiment and theory was 6 dB at one frequency. Surprisingly, the flat-baffle model produced better agreement with experimental results than did the sphere model.

Acoustics↗
PubMed1985

Radiation brain damage induced by interstitial 125I sources: a canine model evaluated by quantitative computed tomography.

The canine brain is a good model of the human brain for studying radiation damage after megavoltage x-irradiation for brain tumors. We have further developed this model to study radiation damage induced by high activity interstitial 125I sources. Removable 125I sources were implanted in normal canine brains, and doses of 1,000 to 10,000 rads were delivered to a reference point at a 10-mm radius from the source; dose rates were 35 to 40 rads/hour at the reference point. Serial quantitative analysis of tissue damage (tissue density and contrast enhancement) was done using computed tomographic scanning up to 6 months after implantation and was compared to histopathological findings after the animals were killed. At doses greater than 19,000 rads (i.e., inside the reference point), frank coagulation necrosis was observed. Pronounced vessel-related changes, manifest as areas of contrast enhancement, corresponded to tissues receiving a minimum of 6,000 rads and a maximum of 19,000 rads. These results indicate that this model can be used in serial noninvasive studies to quantify the development of damage induced by interstitial irradiation and to provide dose-response information in individual animals.

Animals↗
PubMed1984

Relative biological effectiveness of 125I sources in a murine brachytherapy model.

The relative biological effectiveness of 125I and 192Ir has been determined in a murine brachytherapy model that uses a clonogenic cell assay as the end point. Removable 125I or 192Ir sources were implanted at right angles to the surface of RIF-1 tumors grown in the flanks of C3H/He mice. After irradiation for 1-5 days, mice were sacrificed and isodosed annuli of irradiated tumor tissue were sampled for the clonogenic cell assay. The slopes and intercepts of the two radiation survival curves for implanted sources with activities of 10 to 50 Gy for 125I (dose rate = 39.8 +/- 4.3 cGy/hr) and 192Ir (dose rate = 42.3 +/- 2.7 cGy/hr) were identical; the relative biological effectiveness was 1.

Animals↗
PubMed1984

The effect of combination treatment with cis-platinum and low dose rate 125I radiation in a murine brachytherapy model.

We studied the effect of combination treatment with cis-platinum during low dose rate irradiation from 125I sources in the RIF-1 murine flank tumor model. Cell survival measured with a colony forming efficiency assay was used as the experimental endpoint. Sources implanted into tumors delivered 25 Gy of radiation to isodosed annuli of tissue at a dose rate of 1.3 Gy/hr. When 3 mg/kg of cis-platinum was administered 24, 12, and 1 hr before or 0, 12 and 24 hr after irradiation, the effect on cell kill was additive. Thus in the RIF-1 model there is no particular advantage gained by treatment with the combinations of cis-platinum and 125I radiation used in these studies.

Animals↗
PubMed1984

Brachytherapy of recurrent malignant brain tumors with removable high-activity iodine-125 sources.

Thirty-seven patients harboring recurrent malignant primary or metastatic brain tumors were treated by 40 implantations of high-activity iodine-125 (125I) sources. All patients had been treated with irradiation and most had been treated with chemotherapeutic agents, primarily nitrosoureas. Implantations were performed using computerized tomography (CT)-directed stereotaxy; 125I sources were held in one or more afterloaded catheters that were removed after the desired dose (minimum tumor dose of 3000 to 12,000 rads) had been delivered. Patients were followed with sequential neurological examinations and CT scans. Results of 34 implantation procedures were evaluable: 18 produced documented tumor regression (response) for 4 to 13+ months; five, performed in deteriorating patients, resulted in disease stability for 4 to 12 months. The overall response rate was 68%. In 11 patients, implantation did not halt clinical deterioration. At exploratory craniotomy 5 to 12 months after implantation, focal radiation necrosis was documented in two patients whose tumor had responded initially and then progressed, and in three patients whose disease had progressed initially (four glioblastomas, one anaplastic astrocytoma); histologically identifiable tumor was documented in two of these patients. All improved after resection of the focal necrotic mass and are still alive 10, 15, 19, 24, and 25 months after the initial implantation procedure; only one patient has evidence of tumor regrowth. The median follow-up period after implantation for the malignant glioma (anaplastic astrocytoma and glioblastoma multiforme) group is 9 months, with 48% of patients still surviving. While direct comparison with the results of chemotherapy is difficult, results obtained in this patient group with interstitial brachytherapy are probably superior to results obtained with chemotherapy.

Adolescent↗