The Next Linear Collider accelerator will include a large (kilometer scale) and complex collimation system. The size and complexity of this system could be reduced if the collimator jaws could be made immune to damage from the electron beam. We describe two collimation systems currently under development. Construction of a prototype system which uses wheels that can be moved to a new position a...

Introduction: This study investigates basic dosimetric properties of unflattened 6 MV photon beam shaped by multileaf collimator and compares them with those of flattened beams.Materials and Methods: Monte Carlo simulation model using BEAM code was developed for a 6MV photon beam based on Varian Clinic 600 unique performance linac operated with and without a flattening filter in beam line. Dosi...

As people study more facts about a concept, it takes longer to retrieve a particular fact about that concept. This fan effect (Anderson, 1974) has been attributed to competition among associations to a concept. Alternatively, the mental-model theory (Radvansky & Zacks, 1991) suggests that the fan effect disappears when the related concepts are organized into a single mental model. In the presen...

Ginga and Rossi X-ray Timing Explorer (RXTE) observations have allowed an unprecedented view of the recurrent systematic pulse shape changes associated with the 35-day cycle of Hercules X-1, a phenomenon currently unique among the known accretion-powered pulsars. We present observations of the pulse shape evolution. An explanation for the pulse evolution in terms of a freely precessing neutron ...

Abstract. In recent years, volumetric modulated arc therapy (VMAT) has been becoming a more and more important radiation technique widely used in clinical application for cancer treatment. One of the key problems in VMAT is treatment plan optimization, which is complicated due to the constraints imposed by the equipment involved. In this paper, we consider a model with four major constraints: t...

This thesis addresses the problem of reconstructing static objects in 2D and 3D transmission computed tomography (CT). After reviewing the classical CT reconstruction theory, we discuss and thoroughly evaluate various novel reconstruction methods, two of which are original. Our first original approach is for 2D CT reconstruction from full-scan fan-beam data, i.e., for 2D imaging in the geometry...

In this paper, we consider tomographic reconstruction for axially symmetric objects from a single radiograph formed by fan-beam X-rays. All contemporary methods are based on the assumption that the density is piecewise constant or linear. From a practical viewpoint, this is quite a restrictive approximation. The method we propose is based on high-order total variation regularization. Its main a...