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Communication Dans Un Congrès Année : 2006

Expert optimisation of beam orientation and quality controls for intensity-modulated radiotherapy (IMRT)

Résumé

Introduction: IMRT is mainly used for prostate and head-and-neck cancer treatments, because it can achieve an improved compromise between target coverage and organs at risk (OARs) sparing, compared with conformal radiotherapy. Nevertheless, only a small proportion of patients are currently treated with IMRT technique. The main reason is the excessive time required to perform the treatment preparation. The purpose of our study is to streamline the process thereby permitting an increase in the number of patients treated with IMRT. So, our two aims are firstly to optimise and automate beam orientation, and secondly to implement quality control optimisation, using Statistical Process Control (SPC). Methods: Beam orientation optimisation: We studied different optimisation algorithms, such as the simulated annealing, the genetic algorithm and the simplex algorithm, that would help to automatically find the optimal beam arrangement thereby achieving the best compromise between target coverage and OARs sparing. These algorithms require a well-defined score function which formalises the clinical goals to objectively evaluate the figures of merit for different IMRT plans. When beam orientation optimisation is concerned, plan evaluation based on dose criteria is time-consuming. Indeed, the fluence map ought to be optimised for every trial beam configuration. So a score function, based on geometrical criteria, can be introduced as a filter which reduces the search space before a more accurate score function based on dose criteria is used. The geometrical criteria aims to quantify, from a given beam angle, the proportion of irradiated target volume compared to the proportion of irradiated OARs and healthy tissues. Statistical Process Control (SPC) for IMRT quality assurance: SPC is a method currently used in industry for controlling and improving the quality of a process through statistical analysis. In this work, SPC is applied to quality assurance in IMRT, for the comparison between the measured dose and the calculated dose. The aims are: (1) to evaluate and if necessary improve the stability of the system when controlling all beams for one patient (100% control), (2) to determine - when the system is shown to be stable - if we can avoid this 100% control and also how to streamline the process by acting on the number and frequencies of controls, according to predefined statistical risks, instead of choosing them only by experience or intuition, and (3) to anticipate and prevent any deviations of the target values or of their dispersion, using statistical control charts. Discussion: The SPC results show that both the stability and the capability of our process need to be improved. To do this, a retrospective analysis of the results is in progress. If the degree of modulation is shown to be a potential cause of the process instability, we will try to incorporate this knowledge in the beam orientation optimisation score function.

Domaines

Biophysique
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Dates et versions

hal-00118433 , version 1 (05-12-2006)

Identifiants

  • HAL Id : hal-00118433 , version 1

Citer

Karine Gerard, Pierre Aletti, Alain Noel, Hanna Kafrouni, Vincent Marchesi, et al.. Expert optimisation of beam orientation and quality controls for intensity-modulated radiotherapy (IMRT). Oct 2006, pp.82. ⟨hal-00118433⟩
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