A study was performed to determine the relative advantage of computer-controlled couch movement versus manual repositioning to correct patient setup error measured using an electronic portal imaging device (EPID). Twenty-eight on-line setup adjustment trials of anterior-posterior (AP) pelvic projections were evaluated, with 13 setups corrected by automated couch movement determined by direct fe...

In intensity modulated radiation treatments (IMRT), the position of the field edges and the modulation within the beam are often achieved with a multileaf collimator (MLC). During the MLC calibration process, due to the finite accuracy of leaf position measurements, a systematic error may be introduced to leaf positions. Thereafter leaf positions of the MLC depend on the systematic error introd...

Accurate alignment of linear accelerator table rotational axis with radiation isocenter is critical for noncoplanar radiotherapy applications. The purpose of the present study is to develop a method to align the table rotation axis and the MV isocenter to submillimeter accuracy. We developed a computerized method using electronic portal imaging device (EPID) and measured alignment stability ove...

PURPOSE To develop a method for removing the effect of support arm backscatter from Varian electronic portal imaging devices (EPIDs), improving the dosimetric abilities of the imager. METHODS A physical, kernel based model of the backscatter signal produced during an exposure was developed. The model parameters were determined through an optimization process, comparing measured images without...

this research investigates factors of enterprise portals of governmental organizations of iran. methods used in this research are literature and descriptive survey. data was gathered by a researcher-made checklist for enterprise portal factors in the enterprise portals of governmental organizations of iran. the checklist contains six factors that are content management, document management, col...

A model has been developed to describe the sampling process that occurs when intensity modulated radiotherapy treatments (delivered with a multileaf collimator) are imaged with an electronic portal imaging device that acquires a set of frames with a finite dead-time between them. The effects of the imaging duty cycle and frame rate on the accuracy of dosimetric verification have been studied. A...

The desire to increase the precision in radiotherapy delivery has led to the development of advanced imaging systems such as amorphous silicon (a-Si)-based electronic portal imaging, and kV and MV cone beam CT. These are used prior to the delivery of radiation to visualise the organ to be treated and to ensure that the patient setup and treatment delivery are accurate. However, little attention...

Radiotherapy employs high energy radiation for the purpose of cancer treatment. Precise patient positioning is essential with the current use of complicated treatment plans. Portal imaging is often used for pre and during treatment anatomical setup verification. Currently the most advanced and widely used amorphous silicon Electronic portal imaging device (EPID) (aSi 1000) and the TrueBeam line...

Portal dosimetry (PD) was performed for 181 fields from 14 IMRT plans of various clinical sites at gantry zero and source-to-detector distance (SDD) of 100 cm. PD was realized using aSi1000 electronic portal imaging device (EPID) and portal dose prediction (PDP) algorithm implemented in Eclipse treatment planning system (TPS). Agreement of PDP predicted and EPID measured photon fluence/dose dis...

a-Si Electronic Portal Imaging Device (EPID) is an important tool to verify the location of the radiation therapy beam with respect to the patient anatomy. But, Electronic Portal Images (EPI) suffer from low contrast. In order to have better in-treatment images to extract relevant features of the anatomy, image processing tools need to be integrated in the Radiology systems. The goal of this re...