Biomedical subjects

J Drouard

Publications and source records attributed to J Drouard.

3 recordsLinked to original sources

PubMed2000

Dose calculation and verification of intensity modulation generated by dynamic multileaf collimators.

While the development of inverse planning tools for optimizing dose distributions has come to a level of maturity, intensity modulation has not yet been widely implemented in clinical use because of problems related to its practical delivery and a lack of verification tools and quality assurance (QA) procedures. One of the prerequisites is a dose calculation algorithm that achieves good accuracy. The purpose of this work was twofold. A primary-scatter separation dose model has been extended to account for intensity modulation generated by a dynamic multileaf collimator (MLC). Then the calculation procedures have been tested by comparison with carefully carried out experiments. Intensity modulation is being accounted for by means of a 2D (two-dimensional) matrix of correction factors that modifies the spatial fluence distribution, incident to the patient. The dose calculation for the corresponding open field is then affected by those correction factors. They are used in order to weight separately the primary and the scatter component of the dose at a given point. In order to verify that the calculated dose distributions are in good agreement with measurements on our machine, we have designed a set of test intensity distributions and performed measurements with 6 and 20 MV photons on a Varian Clinac 2300C/D linear accelerator equipped with a 40 leaf pair dynamic MLC. Comparison between calculated and measured dose distributions for a number of representative cases shows, in general, good agreement (within 3% of the normalization in low dose gradient regions and within 3 mm distance-to-dose in high dose gradient regions). For absolute dose calculations (monitor unit calculations), comparison between calculation and measurement reveals good agreement (within 2%) for all tested cases (with the condition that the prescription point is not located on a high dose gradient region).

Algorithms↗

PubMed1997

Quality assurance in conformal radiotherapy: DYNARAD consensus report on practice guidelines.

BACKGROUND AND PURPOSE: Conformal radiotherapy has only recently been widely implemented. Although not all aspects have yet been adequately proven, it is generally recognized that maintaining a high degree of precision throughout the process is critical to the treatment outcome while the focus for quality assurance and quality improvement will need to concentrate more on human factors, procedures, communication, organization and training. A general consensus document on quality assurance guidelines for institutions that deliver conformal radiotherapy treatments to patients has been elaborated within the framework of the DYNARAD/BIOMED concerted action on conformal radiotherapy. The present paper aims to highlight those issues that were identified as of specific importance to conformal radiotherapy. The work reported here further details this guidance by direct correlation with the issues involved in the special case of conformal radiotherapy. METHODS: The DYNARAD document has been drafted in the form of a desktop guide comprising six sets of guidelines and is based on the ESTRO advisory report on 'Quality Assurance in Radiotherapy'. RESULTS AND CONCLUSIONS: The document has been endorsed by the DYNARAD group of institutions. As such it can form the basis for further discussions and enter into the subsequent phase of expanding its consensus basis.

Consensus Statements as Topic↗

PubMedDate not supplied

[Evaluation of radiation doses during radiological tests].

The purpose of this document is to provide radiologists with a simple, but realistic means of determining the individual dose delivered to a patient during a radiological examination both in the region under investigation and at any other particularly sensitive organs. Fourteen types of examinations were considered corresponding to those most frequently carried out in France. The choice of examinations and methods of taking the films approaches as closely as possible, the average situations, and the frequency of different techniques is influenced by the results of a national study of radiodiagnostic examinations carried out in France in 1982. In the first section, the influence on the radiation dose of varying different physical parameters and techniques is analysed, with an aim of defining the limits of validity of the presented dosimetric values and the possible adaptation of these values to any individual situation, which is slightly different from these considered in this study. The second section describes the model used for determining the absorbed dose presented in the tables, concerning each type of examination, as well as bibliographic references referring to methods and results of determining the dose. The suggested calculation model may be used as a base for dose estimation for other types of examination.

Abdomen↗