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Biomedical subjects

G Barest

Publications and source records attributed to G Barest.

10 recordsLinked to original sources
PubMed2007

Dental and facial bone abnormalities in pyknodysostosis: CT findings.

Pyknodysostosis is an autosomal-recessive disorder of osteoclast dysfunction causing osteosclerosis, with associated maxillofacial anomalies. Multidetector CT with multiplanar and 3D reconstruction illustrated the pathologic findings in this case. Abnormalities included multiple retained deciduous teeth, unerupted teeth with associated follicles, an irregularly expanded alveolus and body of the mandible, and an obtuse mandibular angle. Volume-rendered imaging better delineated the irregular dentition, with crowding and retention of deciduous teeth.

Adult↗
PubMed2001

Comparison of diameter and perimeter methods for tumor volume calculation.

PURPOSE: Lesion volume is often used as an end point in clinical trials of oncology therapy. We sought to compare the common method of using orthogonal diameters to estimate lesion volume (the diameter method) with a computer-assisted planimetric technique (the perimeter method). METHODS: Radiologists reviewed 825 magnetic resonance imaging studies from 219 patients with glioblastoma multiforme. Each study had lesion volume independently estimated via the diameter and perimeter methods. Cystic areas were subtracted out or excluded from the outlined lesion. Inter- and intrareader variability was measured by using multiple readings on 48 cases. Where serial studies were available in noncystic cases, a mock response analysis was used. RESULTS: The perimeter method had a reduced interreader and intrareader variability compared with the diameter method (using SD of differences): intrareader, 1.76 mL v 7.38 mL (P < .001); interreader, 2.51 mL v 9.07 mL (P < .001) for perimeter and diameter results, respectively. Of the 121 noncystic cases, 23 had serial data. In six (26.1%) of those 23, a classification difference occurred when the perimeter method was used versus the diameter method. CONCLUSION: Variability of measurements was reduced with the computer-assisted perimeter method compared with the diameter method, which suggests that changes in volume can be detected more accurately with the perimeter method. The differences between these techniques seem large enough to have an impact on grading the response to therapy.

Brain↗
PubMed1991

Interinstitutional experience in verification of external photon dose calculations.

Under the auspices of NCI contracts, four institutions have collaborated to assess the accuracy of the pixel-based dose calculation methods they employ for external photon treatment planning. The approach relied on comparing calculations using each group's algorithm with measurements in phantoms of increasing complexity. The first set of measurements consisted of ionization chamber measurements in water phantoms in normally incident square fields, an elongated field, a wedged field, a blocked field, and an obliquely incident beam. The second group of measurements was carried out using thermoluminescent dosimeters in phantoms designed to investigate the effects of surface curvature, high density heterogeneities, and low density heterogeneities. The final study tested the entire treatment planning system, including CT data conversion, in an anthropomorphic phantom. Overall, good agreement between calculation and measurements was found for all algorithms. Regions in which discrepancies were observed are pointed out, areas for algorithm improvement are identified and the clinical import of algorithm accuracy is discussed.

Humans↗
PubMed1991

Three-dimensional photon treatment planning for Hodgkin's disease.

A multi-institutional study was undertaken using computerized planning systems to develop three-dimensional (3-D) radiotherapy plans for Hodgkin's disease (H.D.). Two patients, the first afflicted with bulky stage II disease and another one with early stage I H.D., were studied. Three main categories of plan were produced for each patient: a) a traditional plan which modelled a conventional mantle treatment on the 3-D system, b) a 3-D standard plan where anterior and posterior fields were designed to cover 3-D target volumes, and c) a 3-D unconstrained plan where innovational techniques were employed. Three-dimensional planning provides information about the dose distribution throughout the large volume irradiated in patients with H.D. that is not available with conventional mantle planning. The use of 3-D techniques resulted in improved tumor coverage, but by allowing for uncertainties such as motion, the doses to normal tissues tended to be higher. The use of unorthodox beam arrangements introduced added complexities, and further increased the lung doses. The most even dose distributions were obtained by incorporating compensating filters into anterior fields. Clinicians showed wide variations in their assessment of the plans, possible reasons for which are addressed in this paper. In addition, calculated probabilities from models of tumor control and normal tissue damage are also presented.

Hodgkin Disease↗
PubMed1991

Three-dimensional treatment planning for lung cancer.

The experience of four institutions involved in a three-dimensional treatment planning contract (NCI) for lung cancer is described. It was found that three-dimensional treatment planning has a significant potential for optimization of treatment plans for radiotherapy of lung cancer both for tumor coverage and sparing of critical normal tissues within the complex anatomy of the human thorax. Evaluation tools, such as dose-volume histograms, and three-dimensional isodose displays, such as multiple plane views, surface dose displays, etc., were found to be extremely valuable in evaluation and comparison of these complex plans. It is anticipated that with further developments in three-dimensional simulation and treatment delivery systems, major progress towards uncomplicated local regional control of lung cancer may be forthcoming.

Humans↗
PubMed1990

Treatment planning for internal radionuclide therapy: three-dimensional dosimetry for nonuniformly distributed radionuclides.

A calculational approach is described that provides the spatially varying radiation absorbed dose, presented as isodose contours superimposed on CT images, from nonuniform and/or irregular cumulated activity distributions. CT images are read from magnetic tape and are displayed on a high-resolution color graphics display monitor. Source tissue geometries are defined on a series of contiguous CT images automatically (by an edge detection algorithm) or manually (using a trackball), thereby obtaining a three-dimensional representation of the various source volumes of activity. Dose calculations are performed using a radionuclide-specific absorbed dose point kernel in the form of a lookup table. The method described yields the spatially varying dose delivered to tumor and normal tissue volumes from a patient-specific cumulated activity distribution in a clinically implementable manner. This level of accuracy in determining normal tissue and tumor doses may prove valuable in the evaluation and implementation of radionuclides and radiolabeled compounds for therapeutic purposes.

Algorithms↗
PubMed1988

A comprehensive three-dimensional radiation treatment planning system.

A comprehensive software system has been developed to allow 3-dimensional planning of radiation therapy treatments using the extensive anatomical information made available by imaging modalities such as CT and MR. Biological structures of interest and tumor volumes are defined by outlines drawn on a sequence of CT slices. Beam set-ups may then be determined in three dimensions by displaying the structure contours in a beam's eye view, or in two dimensions using a single CT cut. Each beam defined may be shaped by the specification of block aperture contours, and its intensity may be modified with the use of planar compensators. 3D dose calculation algorithms are discussed. To evaluate the calculation results, dose volume histograms are provided, as well as various types of displays in two and three dimensions, including dose on arbitrarily oriented planes, dose on the surface of anatomical objects, and isodose surfaces. Computer generated beam films are also available as an aid in patient set-up verification. These tools, and others, provide the basis for a comprehensive 3D system that can be used throughout the treatment planning process.

Humans↗
PubMed1987

Arbitrary oblique image sections for 3-D radiation treatment planning.

Methods for selecting and computing arbitrary image sections for displaying anatomic and isodose information for three-dimensional treatment planning are investigated. Selection of the desired plane may be made by defining a plane that is perpendicular to an existing image section (called the base image) and passing through a line on the base image. Alternatively, the anatomic structures displayed perspectively in three dimensions as a series of contours that can be rotated and translated may be used to define an arbitrary plane for image reconstruction. The viewing screen is considered to be the plane of interest. As a typical three-dimensional image of 30 to 60 sections requires considerable computer storage (on the order of 25 megabytes), a reconstruction algorithm may need extensive memory space or CPU and disk I/O time. Of the schemes examined, we believe the following is the most efficient. One pair of images is read from the disk at a time in sequence and intersections of the rows of the cutting plane with the box formed by the consecutive images are computed. Pixel values of all points between the given images are computed by interpolation. Special cases, such as the cutting plane being parallel to or coincident with an existing image, must be considered separately.

Algorithms↗