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Biomedical subjects

E Alexander

Publications and source records attributed to E Alexander.

306 records · Page 17Linked to original sources
PubMedDate not supplied

Radiosurgery for primary malignant brain tumors.

Despite the ability of surgery, radiotherapy, and chemotherapy to prolong survival in patients with glioblastoma multiforme (GBM), most patients succumb to their disease, usually as a result of local tumor persistence or recurrence. Stereotactic radiosurgery (SRS) allows a substantial increase in total dose at sites of greatest tumor cell density while sparing most of the normal brain, resulting in significantly improved survival. SRS was designed as a technique to deliver a large single dose of radiation to a small and focal target: two of its hallmarks are the focal distribution of dose and the inverse relationship between dose and volume. Acute complications of SRS are related to edema and are manifested as a worsening of pre-existing symptoms: seizure, aphasia, and motor deficits--these are treatable with steroids and are transient in the majority of cases. The actuarial risk of undergoing reoperation was 33% at 12 months and 48% at 24 months, following SRS. Patterns of failure were similar following brachytherapy or SRS as treatment for recurrent GBM with most patients experiencing marginal failure outside the original treatment volume. Patients with small (< 30 mm diameter), radiographically distinct and focally recurrent GBM should be considered for SRS. Larger lesions (> 30 mm diameter), especially those adjacent to eloquent cortex or critical white matter pathways, must be evaluated with caution. The potential for acute toxicity associated with SRS increases substantially for larger lesions. There is a significant survival advantage using SRS in many patients with gliomas, especially if appropriately used with surgery and other adjuvant therapy.

Brachytherapy↗
PubMedDate not supplied

Evaluation of intracranial cysts by intraoperative MR.

Eleven patients with intracranial cystic collections were evaluated in the open-bore intraoperative MR system. In each case, the cystic collection or the surrounding cerebrospinal fluid (CSF) space was injected with .02 to .5 cc of .5 mol/l gadopentetate dimeglumine. Serial imaging was performed using T1-weighted imaging. In seven patients, free communication was demonstrated between the cystic collection and the surrounding CSF spaces. In four cases, the cyst did not communicate with the CSF; two of these were drained in the intraoperative MR system with reduction in symptoms. One patient developed an aseptic meningitis 10 days after the study, which was successfully treated with steroids; no other complications were noted. We conclude that the communication of intracranial cystic collections with the cisterns and ventricles can be safely and effectively elucidated with gadolinium injection in the intraoperative MR system.

Adult↗
PubMedDate not supplied

Intraoperative dynamic MRI: localization of sites of brain tumor recurrence after high-dose radiotherapy.

In patients with malignant astrocytomas or metastatic brain disease treated with high-dose radiotherapy, conventional imaging methods may not adequately distinguish recurrent tumor from radiation change. We used a fast spoiled gradient refocusing technique in the open-configuration intraoperative MR system to assess the rate of regional enhancement of the treated tumor bed and to localize specific sites for pathologic sampling to determine whether gadolinium uptake correlated with histologic data. Twenty-four patients were studied. Fourteen of 15 patients with areas of early enhancement had recurrent tumor present in histologic samples, and 8 of the remaining 9 patients had only reactive changes. Dynamic MRI was predictive of recurrent tumor (P < .0005, Fisher exact test and P < .002, Student t test). We conclude that dynamic MRI in the open-bore magnet is a promising method for localizing potential sites of active tumor growth in patients treated for malignant astrocytomas and metastatic brain lesions.

Brain↗
PubMedDate not supplied

Dose-volume histogram computations for small intracranial volumes.

A sampling formalism is presented to accurately compute the absolute volumes and integral dose-volume histograms of small volumes treated in stereotactic radiosurgery. The presence of small volumes and sharp dose gradients places special constraints on the computational formalism and the accuracy required to compute the dose-volume relationships. We use a spatially nonuniform random sampling method to allow an efficient and accurate computation of the dose-volume histograms for an arbitrary number of volumes. The computation of absolute volume vs dose allows intercomparison of dose delivered to target and dose-critical volumes and allows a quantitative trade-off analysis often critical to an optimal treatment of the lesion.

Algorithms↗
PubMedDate not supplied

Radiation necrosis vs high-grade recurrent glioma: differentiation by using dual-isotope SPECT with 201TI and 99mTc-HMPAO.

Conventional imaging techniques are often unreliable in distinguishing between radiation necrosis and recurrent glioma in patients who are symptomatic after high-dose radiotherapy. We performed dual-isotope single-photon emission computed tomography (SPECT) with the use of thallium-201 (201TI) and the perfusion agent 99mTc-hexamethyl-propyleneamine oxime (HMPAO) to aid in this differentiation in 15 patients with glioma prior to biopsy. We found that dual-isotope SPECT scanning correlated with the pathologic findings in 14 of the 15 cases. All patients with high 201TI uptake in their treated tumor beds had local tumor recurrence, and all patients with low 201TI uptake showed only radiation changes without evidence of solid tumor. In patients with an intermediate level of 201TI concentration in their tumor bed, 99mTc-HMPAO uptake differentiated those patients with active tumor from those without; three of four patients with preserved or increased perfusion had pathologic evidence of solid tumor, whereas none of the four patients with decreased perfusion to the tumor bed had evidence of local recurrence. We believe that dual-isotope SPECT with 201TI and 99mTc-HMPAO may be useful in differentiating sites of likely tumor growth from nonspecific radiation changes in patients treated for malignant glioma.

Adolescent↗
PubMedDate not supplied

First coitus for adolescents: understanding why and when.

BACKGROUND: Correlates of initiation of coitus for teenagers were examined, and participants were asked their reasons for initiating or postponing the onset of coitus. METHODS: Questionnaires were completed privately by 218 patients aged 13 to 18 years. Questions explored the reasons adolescents cite for their sexual decisions and the role of peer influence in these decisions. RESULTS: Correlation was noted in young teenagers between perception of peer sexual behavior and participant's initiation of coitus. Reasons stated for engaging in first intercourse reflect both active choices and loss of control. Reasons for refraining included fear of pregnancy and sexually transmitted diseases, lack of developmental readiness and opportunity, and social sanctions. Morality was cited infrequently as a reason for postponing sexual behavior. CONCLUSIONS: Results suggest that sexuality education should address the direct and curious questions of younger teenagers about sexuality, help youth define strategies that they can use to evaluate and resist peer pressure, and give more generalized attention to ways of helping youth feel competent. Physicians and other health educators might focus on helping older youth define how and when they know they are ready to have intercourse, consider ways of expressing sexuality that do not jeopardize health, and improve communication skills when talking with friends and potential partners about sexual issues.

Adolescent↗