879 research outputs found
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Resection Cavity Contraction Effects in the Use of Radioactive Sources (1-25 versus Cs-131) for Intra-Operative Brain Implants.
Background and Objectives Intra-parenchymal brain surgical resection cavities usually contract in volume following low dose rate (LDR) brachytherapy implants. In this study, we systematically modeled and assessed dose variability resulting from such changes for I-125 versus Cs-131 radioactive sources. Methods Resection cavity contraction was modeled based on 95 consecutive patient cases, using surveillance magnetic resonance (MR) images. The model was derived for single point source geometry and then fully simulated in 3D where I-125 or Cs-131 seeds were placed on the surface of an ellipsoidal resection cavity. Dose distribution estimated via TG-43 calculations and biological effective dose (BED) calculations were compared for both I-125 and Cs-131, accounting for resection cavity contractions. Results Resection cavity volumes were found to contract with an effective half-life of approximately 3.4 months (time to reach 50% of maximum volume contraction). As a result, significant differences in dose distributions were noted between I-125 and Cs-131 radioactive sources. For example, when comparing with static volume, assuming no contraction effect, I-125 exhibited a 31.8% and 30.5% increase in D90 and D10 values (i.e., the minimal dose to 90% and 10% of the volume respectively) in the peripheral target areas over the follow-up period of 20.5 months. In contrast, Cs-131 seeds only exhibited a 1.44% and 0.64% increase in D90 and D10 values respectively. Such discrepancy is likewise similar for BED calculations. Conclusion Resection cavity contractions affects Cs-131 dose distribution significantly less than that of I-125 for permanent brain implants. Care must be taken to account for cavity contractions when prescribing accumulative doses of a radioactive source in performing the brain implant procedures
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Patient-Specific Fetal Dose Determination for Multi-Target Gamma Knife Radiosurgery: Computational Model and Case Report.
A 42-year-old woman at 29 weeks gestation via in vitro fertilization who presented with eight metastatic brain lesions received Gamma Knife stereotactic radiosurgery (GKSRS) at our institution. In this study, we report our clinical experience and a general procedure of determining the fetal dose from patient-specific treatment plans and we describe quality assurance measurements to guide the safe practice of multi-target GKSRS of pregnant patients. To estimate fetal dose pre-treatment, peripheral dose-to-focal dose ratios (PFRs) were measured in a phantom at the distance approximating the fundus of uterus. Post-treatment, fetal dose was calculated from the actual patient treatment plan. Quality assurance measurements were carried out via the extrapolation dosimetry method in a head phantom at increasing distances along the longitudinal axis. The measurements were then empirically fitted and the fetal dose was extracted from the curve. The computed and measured fetal dose values were compared with each other and associated radiation risk was estimated. Based on low estimated fetal dose from preliminary phantom measurements, the patient was accepted for GKSRS. Eight brain metastases were treated with prescription doses of 15-19 Gy over 143 min involving all collimator sizes as well as composite sector mixed shots. Direct fetal dose computation based on the actual patient's treatment plan estimated a maximum fetal dose of 0.253 cGy, which was in agreement with surface dose measurements at the level of the patient's uterine fundus during the actual treatment. Later phantom measurements also estimated fetal dose to be in the range of 0.21-0.28 cGy (dose extrapolation curve R2 = 0.998). Using the National Council on Radiation Protection and Measurements (NCRP) population-based model, we estimate the fetal risk of secondary malignancy, which is the primary toxicity after 25 weeks gestation, to be less than 0.01%. Of note, the patient delivered the baby via scheduled cesarean section at 36 weeks without complications attributable to the GKSRS procedure. GKSRS of multiple brain metastases was demonstrated to be safe and feasible during pregnancy. The applicability of a general patient-specific fetal dose determination method was also demonstrated for the first time for such a treatment
Math in the Dark: Tools for Expressing Mathematical Content by Visually Impaired Students
Blind and visually impaired students are under-represented in the science, technology, engineering, and mathematics disciplines of higher education and the workforce. This is due primarily to the difficulties they encounter in trying to succeed in mathematics courses. While there are sufficient tools available to create Braille content, including the special Nemeth Braille used in the U.S. for mathematics constructs, there are very few tools to allow a blind or visually impaired student to create his/her own mathematical content in a manner that sighted individuals can use. The software tools that are available are isolated, do not interface well with other common software, and may be priced for institutional use instead of individual use. Instructors are unprepared or unable to interact with these students in a real-time manner. All of these factors combine to isolate the blind or visually impaired student in the study of mathematics. Nemeth Braille is a complete mathematical markup system in Braille, containing everything that is needed to produce quality math content at all levels of complexity. Blind and visually impaired students should not have to learn any additional markup languages in order to produce math content.
This work addressed the needs of the individual blind or visually impaired student who must be able to produce mathematical content for course assignments, and who wishes to interact with peers and instructors on a real-time basis to share mathematical content. Two tools were created to facilitate mathematical interaction: a Nemeth Braille editor, and a real-time instant messenger chat capability that supports Nemeth Braille and MathML constructs. In the Visually Impaired view, the editor accepts Nemeth Braille input, displays the math expressions in a tree structure which will allow sub-expressions to be expanded or collapsed. The Braille constructs can be translated to MathML for display within MathType. Similarly, in the Sighted view, math constructs entered in MathType can be translated into Nemeth Braille. Mathematical content can then be shared between sighted and visually impaired users via the instant messenger chat capability.
Using Math in the Dark software, blind and visually impaired students can work math problems fully in Nemeth Braille and can seamlessly convert their work into MathML for viewing by sighted instructors. The converted output has the quality of professionally produced math content. Blind and VI students can also communicate and share math constructs with a sighted partner via a real-time chat feature, with automatic translation in both directions, allowing VI students to obtain help in real-time from a sighted instructor or tutor. By eliminating the burden of translation, this software will help to remove the barriers faced by blind and VI students who wish to excel in the STEM fields of study
A compilation, classification, and comparison of lists of spontaneous speaking vocabulary of children in kindergarten, Grade I, Grade II, and Grade III
Thesis (Ed.M.)--Boston UniversityLanguage development has been studied for many years.
The beginning vocabularies are easy to count ana record.
As tne child grows and moves about, his speaking vocabulary
increases very rapidly. Some estimates suggest
that a minimum speaking vocabulary at six years would include
three thousand words.
New words have come into children's speaking vocabularies
as a result of modern technology since World War II.
Lists of spontaneous vocabulary furnish material for teachers
and text book writers. The purpose of this study is
to analyze two lists recorded in 1954 and 1955.
An attempt has been made to classify the new list.
The lists were compared with three existing lists, Rinsland,
International Kindergarten Union and Gates
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