Biomedical subjects

P Therrien

Publications and source records attributed to P Therrien.

4 recordsLinked to original sources

PubMed1992

A numerical method for electron transport calculations.

A numerical algorithm for calculating the penetration of electrons in dense media is presented. The numerical algorithm is intended for future application to radiotherapy dose calculations. The method is generic in the sense that it may be used with different theoretical models describing the angular scattering of electrons with depth. It is also general enough that it may be applied to electron dose calculations in heterogeneous as well as homogeneous media. The assumptions used in the algorithm are examined and equations describing the evolution of the distribution of electrons with depth are presented. Calculations have been performed for 10 MeV broad beams and pencil beams incident on water. It is shown that the Fermi-Eyges analytical solutions are recovered if the angular scattering process is assumed to be a Gaussian Markov process and the cumulative angle of electron travel remains small. In the case where the small angle approximation is not imposed, the numerical method qualitatively reproduces, at large depths, the wide angle scattering 'tails' seen in Monte Carlo generated profiles.

Algorithms↗

PubMed1990

Treatment planning for protocol-based radiation therapy.

Many protocol studies are conducted in which patients are assigned to alternative treatment regimens. Typically the dosimetric specifications will define the maximal and minimal target doses and maximal doses to specified critical normal structures, and the success of the study will depend upon the consistency and reliability with which these dose specifications are applied. We have investigated the use of dose-area histograms to ensure complete adherence to protocol dose specifications. A dose prescription is prepared that defines upper and lower target doses as well as normal tissue dose tolerance levels for all organs of interest. In addition, dose-volume histograms are derived which provide quantitative measures of the extent to which each dose limit has been met. This technique can be used during treatment planning to prevent protocol violations of pre-defined severity, or for retroactive correlation of local tumor recurrence and treatment-related morbidity with dose levels in the target and normal tissues. An example is presented for a protocol study of ca prostate, stages A and B, in which seven treatments were evaluated at the mid-plane for protocol violations.

Clinical Trials as Topic↗

PubMed1988

The objective evaluation of alternative treatment plans: I. Images of regret.

An innovative approach to treatment planning is described in which a planned dose distribution is evaluated in terms of prescribed limits of acceptability, and any discrepancies (referred to as "regions of regret") are displayed in the form of a contour diagram in which colors are used to represent different types and degrees of regret. A commercial treatment planning system has been modified to display images of regret in addition to conventional isodose plots, and is used for the comparison of alternative plans in terms of adequate target coverage and minimal irradiation of sensitive organs. Required tumor dose levels and organ-specific tolerance doses are prepared in advance by the clinician for each site and stored in a prescription file for use in the planning process. The method is found to expedite the optimization procedure, is objective and reproducible, and provides clear documentation of the selection process.

Computer Graphics↗

PubMed1987

Colour visualization as an aid to the comparison of treatment plans for prostatic carcinoma.

The conventional treatment plan is usually presented as a longitudinal set of axial cross-sections showing the patient contour and selected anatomical features, together with a set of isodose lines. It is difficult to interpret the correlation between dose, target and organs at risk, and the comparison of several plans is time-consuming and highly subjective. This procedure has been improved by modifying a treatment planning system to provide 'images of regret', in which regions are shown in appropriate colour if the planned dose distribution is at variance with prescribed conditions defining limits of acceptability. The method has been used for planning treatment for localized prostatic cancer, and found to be useful for the rapid selection of the optimal treatment plan from a set of alternatives.

Adenocarcinoma↗