The authors retrospectively analyzed 140 patients treated at the University of California, San Francisco, from 1967 to 1990 to evaluate the results of radiation therapy (median 5400 cGy) given as an adjuvant to subtotal resection of intracranial meningioma. Of the 140 meningiomas, 117 were benign and 23 were malignant. The median follow-up period was 40 months. The overall survival rate at 5 years was 85% for the benign and 58% for the malignant tumor groups (p = 0.02); the 5-year progression-free survival rates were 89% and 48%, respectively (p = 0.001). For patients with benign meningioma, the 10-year overall and progression-free survival rates were 77%. An improved progression-free survival rate in that group was not related to tumor size but was associated with a younger age (p = 0.01) and treatment after 1980 with innovative technologies (p = 0.002); none of those variables affected the progression-free survival rate in the patients with malignant meningioma. Increased progression-free survival in the benign tumor group was also significantly associated with increasing the minimum radiation dose (p = 0.04). The 5-year progression-free survival rate for patients with benign meningioma treated after 1980 (when computerized tomography or magnetic resonance imaging was used for planning therapy) was 98%, as compared with 77% for patients treated before 1980 (p = 0.002). There were no second central nervous system tumors. Morbidity (3.6%) included sudden blindness or cerebral necrosis and death. When total resection of benign meningioma is not feasible, subtotal resection combined with precise treatment planning techniques and adjuvant radiation therapy can achieve results comparable to those of total resection.
The mechanism of photoconductivity in polycrystalline CdS has been studied over the temperature range 100–300 K using Hall-effect and conductivity measurements in the dark and under white light illumination. Samples were prepared in thin film form by spray pyrolysis and as power-binder mixtures. Dark conductivities covered the range 10−9–101 Ω−1 cm−1. Dark conductivity is interpreted in terms of a two-dimensional version of the grain-boundary barrier model developed by Seto for polycrystalline Si. Except at very low carrier densities, Hall mobilities are found to be thermally activated, and intergrain barrier heights φb are derived for spray pyrolysis layers with doping levels covering the range N = 1014–1018 cm−3. A maximum barrier φbmax ≊0.2 Ev is found at a corresponding doping level, Nmax ≊2×1016 cm−3, which represents the situation where the barrier depletion layers just extend through the whole grain. From this we derive a mean grain diameter of 0.3 μm in good agreement with the result of transmission electron microscopy. For samples having N<Nmax the average free carrier density n̄≪N and photoconductivity occurs entirely through an increase in n̄ up to the point where the depletion regions begin to contract away from the center of the grains. For samples having N≳Nmax both μ and n̄ increase. The detailed variations of μ and n̄ are interpreted in terms of the Seto model with the added hypothesis that photogenerated holes are all trapped at grain boundaries. Hall-effect measurements are interpreted on the assumption that the Hall coefficient R measures the average carrier density in the grain, i.e., R = (n̄e)−1, and we note that n̄ may differ significantly from the doping level N, even when N⩾Nmax. Photo-Hall results provide evidence in support of this hypothesis.
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