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Biomedical subjects

D A Larson

Publications and source records attributed to D A Larson.

At least 91 records · Page 5Linked to original sources
PubMed1990

Estimation of complications for linear accelerator radiosurgery with the integrated logistic formula.

Radiosurgery techniques permit high doses of single fraction irradiation to be administered to small volumes of tumor with relative sparing of surrounding brain tissue. The tolerance of surrounding normal brain tissue to dose distributions from linear accelerator radiosurgery with different collimator sizes is an important factor that must be estimated by anyone using these treatment techniques. The exponential and linear quadratic versions of the integrated logistic formula were used to estimate the probability of brain necrosis at different doses for radiosurgical dose distributions administered by a 6 MV linear accelerator with a 5 arc technique for collimator sizes from 12.5 to 30 mm in diameter. Dose-volume isoeffect curves for a 3% risk of brain necrosis from linear accelerator radiosurgery were then calculated. These curves approximate those calculated for gamma knife radiosurgery and a published 1% dose-volume isoeffect line predicted for proton beam irradiation. Similar dose-volume isoeffect curves were calculated for single fraction radiosurgery boosts administered after 30 Gy of whole brain irradiation in 12 fractions. The integrated logistic formula appears to be a useful tool for estimating tolerance and providing guidelines for prescribing radiation doses for linear accelerator radiosurgery.

Brain Diseases↗
PubMed1990

Interstitial brachytherapy.

In the last several years there has been a renewed interest in interstitial brachytherapy for the treatment of both newly diagnosed and recurrent malignant gliomas and solitary cerebral metastases. A variety of techniques are currently in use for the planning and stereotactic implantation of radioactive isotopes into these tumors. Although there seems to be strong evidence to support the use of this technique for recurrent malignant gliomas, further work is needed to confirm its efficacy in an adjuvant setting for treating of newly diagnosed tumors and to determine the effect of the addition of hyperthermia or chemotherapy on outcome.

Brachytherapy↗
PubMed1990

Introduction to radiosurgery.

Although radiosurgery treatments began more than 30 years ago and thousands of patients have been treated, the role of radiosurgery in the treatment of intracranial lesions is continuing to evolve. For AVM several groups have reported favorable angiographic response rates. Further information, however, is needed to establish the relationship between this objective measure of response and the risk of subsequent hemorrhage. Ideally this relationship might be established through randomized trials. For ethical reasons, however, such trials are unlikely to be undertaken. Although radiosurgery may finally prove useful in the treatment of lesions other than AVM, currently available retrospective data do not allow firm conclusions in most cases. Various techniques can be used to deposit the dose accurately in a predetermined intracranial volume. Nonetheless, it frequently is difficult to define the three-dimensional configuration of the volume requiring treatment accurately. This difficulty is independent of the radiosurgical technique used and, together with dose prescription and patient selection, is probably of greater importance than possible differences in dose distribution produced by different systems. Because many patients will have radiosurgery in nontrial clinical settings, it is important that future reports provide sufficient information to allow meaningful interpretation. At minimum, reports must contain an accounting of all patients treated, including number followed and number lost to follow-up evaluation or otherwise lacking repeat radiologic studies or clinical evaluation. (The statement that 1000 patients were treated is not useful in the absence of this accounting and may cast doubt on reported results.) Beyond accounting it is helpful if reports provide (1) information on dimensions and intracranial location of lesions treated and correlation with dose and outcome, (2) quantitative information on dose prescribed, including minimum and maximum dose to the target, especially when multiple isocenters are used (when isodose contours from individual isocenters must be summed), (3) detailed information on patients developing complications (in what ways did their presentation or treatment differ from that of other patients?), and (4) thorough data analysis using modern statistical techniques. The number of radiosurgery facilities is increasing rapidly. Whether the number of patients treated in each facility will continue to rise each year as more new facilities are open is conjectural and will depend on the evolution of indications for radiosurgery and on the evolution of referral patterns as techniques, facilities, and results become established.

Brain Neoplasms↗
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↗
PubMed1989

Volume therapy in orthostatic transient ischemic attacks.

We report the case of an 83-year-old man with recurrent orthostatic transient ischemic attacks despite anticoagulation and crystalloid therapy. An initial cerebral angiogram revealed a nearly occluded right carotid artery with a string sign. Following aggressive volume expansion with albumin, the patient became asymptomatic. A second angiogram demonstrated the resolution of the carotid string sign and unmasked a high-grade, very tight, surgically approachable stenosis. The role of a high intravascular volume status is discussed.

Aged↗
PubMed1988

Delayed traumatic midbrain syrinx. Clinical, pathologic, and electrophysiologic features.

Seven months following severe crushing closed-head trauma with initial excellent recovery, neurologic deficits referable to the right mesencephalon abruptly developed in a 28-year-old man. Computed tomography demonstrated a cystic midbrain lesion with apparent communication with the aqueduct (later confirmed at autopsy). Brain-stem auditory evoked potentials after the clinical deterioration showed depression of amplitude of wave V, compared with predeficit records, only when the ear contralateral to the brain-stem lesion was stimulated.

Adult↗
PubMed1988

Inspiratory muscle training with a pressure threshold breathing device in patients with chronic obstructive pulmonary disease.

The inspiratory pressure load is an important variable in inspiratory muscle training (IMT), but previous studies with chronic obstructive pulmonary disease (COPD) patients have not controlled for this variable. We compared the effects of two months of IMT with a pressure threshold breathing device at inspiratory pressure loads equal to either 15 or 30% of each patient's maximal inspiratory pressure (Plmax). This study was double blind and patients were randomly assigned to the treatment groups, 12 in the 15% group and ten in the 30% group. Dependent variables were measured at baseline, and after one and two months of IMT. Patients who exercised with the 30% load improved the following: Plmax by a mean of -12 +/- 9 cm H2O (p less than 0.01), endurance time while breathing against an inspiratory pressure load equal to 66% of Plmax by 5 +/- 9 min (p less than 0.01), and 12-min distance walk (12MD) by 199 +/- 90 feet (p less than 0.01). Patients who exercised with the 15% load demonstrated no improvements in Plmax, endurance time, and 12MD. There were no changes in patients' report of functional impairment (Sickness Impact Profile), mood (Profile of Mood States), health status (Health Perceptions Questionnaire), and pulmonary symptoms (respiratory symptom log). We conclude that the 30% load was more effective than the 15% load in this sample.

Affect↗
PubMed1987

Neuroschisis of the cervical spinal cord in a patient with Klippel-Feil syndrome.

During the neurological work-up of a young patient with Klippel-Feil syndrome, the presence of a neuroschisis of the cervical spinal cord was detected. The patient presented with a transient and acute hemisensory loss and a Horner's syndrome of the opposite side. The unusual presentation and radiological findings in a patient with Klippel-Feil syndrome prompted this report.

Adult↗
PubMed1985

Early peritoneal mesothelioma: a treatable malignancy.

37 patients with malignant peritoneal mesothelioma were studied to assess the efficacy of combined therapy. 14 patients presented after 1982. Of 6 patients treated intensively, all remain alive with no evidence of disease by computed tomographic scan at 9-36 months. Of 8 patients treated palliatively, 5 are dead. (5 had stable disease, 1 has progressed despite all treatment, and 2 were not treated.) Survival of the intensively treated group is significantly better than that of other stage I patients in this series. Patients under 40 had a significantly better survival rate than older patients.

Adolescent↗
PubMed1985

Treatment of perineural metastasis from squamous carcinoma of the skin with aggressive combination chemotherapy and irradiation.

Perineural metastasis from squamous cell carcinoma is quite rare. The treatment of such metastasis in the head and neck region is difficult due to base of skull or intracranial involvement by tumor. Surgery and radiotherapy may provide local control, but patients often fail distantly. We present a patient with squamous cell carcinoma presenting with perineural metastasis who was successfully treated with combination chemotherapy and definitive radiation therapy. Suggestions of therapeutic management are made of this uncommon clinical problem.

Aged↗
PubMed1984

Influence of monensin on the performance of cattle.

Performance data on nearly 16,000 head of cattle that were used in trials to document effects of monensin on feedlot cattle were summarized. Cattle fed monensin-containing diets gained 1.6% faster, consumed 6.4% less feed and required 7.5% less feed/100 kg gain than cattle fed control diets. Monensin resulted in the greatest improvement in feed/gain at 2.9 Mcal metabolizable energy (ME)/kg diet dry matter (DM). Within the range of monensin concentrations used in the trials that were summarized (31.8 +/- 7.5 mg/kg DM), high monensin concentrations did not improve feed/gain over that obtained with lower concentrations. Carcass characteristics were not significantly influenced by monensin. Responses of cattle to monensin and implants were additive. Energy metabolism data suggested that monensin improved digestibility of DM, reduced fasting heat production and increased dietary net energy maintenance (NEm) values more than it increased net energy gain (NEg) values. Data showing the response of cattle to monensin when fed various dietary protein concentrations or sources of supplemental N suggested that monensin had a protein sparing effect. Monensin has also been shown to reduce lactic acid production, aid in the control of coccidia and bloat and to be toxic to face and horn fly larva in feces of monensin-fed cattle. In pasture trials, monensin improved daily gains. When fed to beef cows, monensin reduced amounts of feed required to maintain cow weight.

Acidosis↗
PubMed1980

Computed tomography of hemorrhage from anterior communicating artery aneurysms, with angiographic correlation.

The CT findings in 19 cases of ruptured anterior communicating artery aneurysms are analyzed and compared to the angiographic appearance. Observations from this series and literature review include (a) occasional negative scans, (b) visualization of non-giant aneurysms on infused axial scans, (c) common asymmetric subarachnoid hemorrhage, (d) involvement of the anterior interhemispheric fissure whenever subarachnoid hemorrhage is visualized, (e) "typical" septal hematoma in a minority of cases, (f) frequent infarction, particularly in the anterior cerebral artery distribution, (g) "meningeal hyperemia" seen on post-contrast scans, and (h) little correlation between angiographic aneurysm orientation and the location of hemorrhage on CT scan.

Adult↗
PubMed1980

Xanthogranuloma of the third ventricle producing hydrocephalus.

Symptomatic xanthogranulomas of the ventricular system are rare entities. Presented here is a case of obstructive hydrocephalus that was caused by a xanthogranuloma arising from the superior aspect of the 3rd ventricle. The operative approach is discussed.

Adult↗