Biomedical subjects

G W Sherouse

Publications and source records attributed to G W Sherouse.

22 records · Page 2Linked to original sources

PubMed1987

A spreadsheet program for brachytherapy planning.

A computer program (brachy-spread) which allows spreadsheet-like interactive adjustment of the loading of any brachytherapy application has been implemented. Sources are collected into objects, each assigned an activity and duration of implant. Activities and times may be adjusted by moving a cursor to the datum to be edited and entering a new value from the keyboard. Alternatively, the desired total dose to a given calculation point may be edited resulting in a recalculation of the time for all objects. For each of a set of calculation points, dose rates, total doses, and the percent contribution of each object to the point are displayed and instantly updated as the times and activities are adjusted. The program design includes rapidly updated display of isodose curves in previously selected arbitrary planes. A strategy for providing rapid dose display involving precalculation of fractional dose tables is used. The program has significantly reduced the time required to determine the appropriate loading of GYN applications and of implants which involve a combination of line sources and seeds.

Algorithms↗

PubMed1987

Automatic digital contrast enhancement of radiotherapy films.

The practice of radiotherapy involves the precise geometric localization of both anatomic and non-anatomic structures using radiographs which are typically of very low contrast. Portal and verification films suffer from poor contrast as a result of the dominance of Compton interactions at therapeutic energies, and implant localization films often are degraded by extreme patient thickness (lateral pelvis) or projection of bony structures (head and neck). Automatic contrast enhancement techniques developed and proven for optimization of the display of digitally produced images such as CT have been applied to radiotherapy films to improve contrast and augment readability. This approach has become viable only recently with the advent of high speed, high resolution film digitizers and laser cameras and the evolution of sufficiently powerful computer hardware.

Brachytherapy↗

PubMedDate not supplied

Coordinate transformation as a primary representation of radiotherapy beam geometry.

An approach to both geometric specification of radiotherapy beams and computerized solution of geometric treatment planning problems using coordinate transformations is presented. It is demonstrated that the specification of the geometric relationship of a treatment beam to a patient can be uniquely given by a 4 x 4 coordinate transformation matrix, and that the matrix representation can be translated from (and to) the more conventional machine-based specification of geometry. This approach enables a compact representation of the patient/beam geometry which is independent of the specific labeling conventions of the treatment machine and which can be directly exploited in the solution of treatment planning problems. Beam geometry can be easily described either in terms of the natural degrees of freedom of a therapy machine or in terms of alternative, problem-specific frames of reference. The ability to use these various frames of reference interchangeably allows the designer of treatment design software to present appropriate task-specific user interfaces for arbitrarily complex tasks, and thus reduce the cognitive burden on users of the software.

Humans↗

PubMedDate not supplied

A mathematical basis for selection of wedge angle and orientation.

The treatment plan optimization criterion that dose be homogeneous over an irradiated volume is equivalent to the criterion that the magnitude of the dose gradient be zero throughout that volume. If the dose gradient due to an individual beam is represented by a vector, the dose gradient due to an ensemble of beams is given by the weighted vector sum of the constituent beams' individual gradients. Given a fixed ensemble of beams, the two ways in which the total dose gradient can be modified are (1) by changes in relative beam weights and/or (2) by changes in the direction and/or magnitude of the dose gradient of one or more of the individual beams. Conventional wedges provide a simple mechanism for altering the dose gradient of a single beam. This paper describes a mathematical basis for the selection of wedge angles, wedge orientations, and relative beam weights, with the goal of producing a field of zero gradient over the volume of beam intersection. The approach is based on 3-dimensional vector analysis of dose gradients, and is valuable not only for its formalism, but also for the conceptual basis it provides for discussing and solving general wedge selection problems.

Biophysical Phenomena↗