Modeling in the leakage radiation of a medical linear accelerator a function of the collimator opening: Analytical extrapolation of the leak field opened by a method semi-empirical based measurement at zero field

Abstract

Introduction The optimization of radiotherapy requires precise knowledge of all sources at the origin of the radiation, even at low doses to healthy tissues of the patient. Currently, the developed analytical models for estimating the doses to healthy tissue based on the assumption that the radiation leakage from a medical linear accelerator would be independent of the collimator opening. However, this hypothesis does not account for a very large number of physical and geometrical aspects of each accelerator. The objective of this work is to propose a more realistic model for accelerators leaks. Materials and methods Themeasurements are performed on a linear accelerator Novalis Tx TM (Varian Medical Systems, Palo Alto, CA, USA). Detectors are used thermoluminescent powder type 7 (TLD700) compounds of powder LiF doped with Mg et Ti provided by the company Equal-Estro Laboratory. Development of computer codes using the libraries: CodeBlocks ® (libraries: OpenGL), Matlab ® et Gnuplot ® . Results Concerning theoretical modeling, the early results give encouraging theoretical distributions. The model is the end of development measures analysis is ongoing and results will be presented and discussed. Overall we see a gradual decrease in leakage with increasing the opening of the collimator. This decrease is even more important that we be near the field. Conclusion Our model can calculate the dose from accelerator of the leakage for any location in the patient and configuration of irradiation.