Optimizing the effective spot size and the dosimetric leaf gap of the AcurosXB algorithm for VMAT treatment planning.

Purpose: The aim of this study is to provide and test a new methodology to adjust the AcurosXB beam model for VMAT treatment plans.

Method: The effective target spot size of the AcurosXB v15 algorithm was adjusted in order to minimize the difference between calculated and measured penumbras. The dosimetric leaf gap (DLG) was adjusted using the asynchronous oscillating sweeping gap tests defined in the literature and the MLC transmission was measured.

A Bayesian control chart based on the beta distribution for monitoring the two-dimensional gamma index pass rate in the context of patient-specific quality assurance.

Purpose: In the context of quality assurance in intensity modulated radiation therapy (IMRT), the aim of this work was two-fold: (a) to show that the beta distribution characterizes the two-dimensional gamma index pass rate (GIPR), and that the quantiles of the distribution should be used in order to compute the control limit (CL) for the detection of abnormally low GIPR, and (b) to introduce a Bayesian control chart that allows calculation of CLs from the first measurement.

Methods: In order to enable monitoring of the GIPR from the first measurement, we developed a Bayesian control chart based on the beta distribution, elaborated according to the following two steps: (a) an iterative bayesian inference approach without any prior information on the GIPR distribution was used at the start of monitoring and the CL was progressively updated; and (b) when sufficient in-control arcs had been recorded and the estimators of the parameters of the beta distribution were sufficiently accurate, the CL of the chart was fixed to a constant value corresponding to the quantile of the beta distribution. The clinical utility of this approach is illustrated through a real data case study: monitoring the GIPR of patients treated with a moving gantry IMRT technique RapidArc on a Novalis TrueBeam STx (Varian Medical Systems) linear accelerator equipped with an aS1200 electronic portal imager device.

Comparison of five dose calculation algorithms in a heterogeneous media using design of experiment.

Purpose: Design of experiments (DoE) provides a methodology to reveal the influence of input values on the measured output with a limited number of trials. The purpose of this study was to describe how DoE can be used to evaluate the performances of several dose calculation systems in heterogeneous media, including algorithms like Pencil Beam (PB), Anisotropic Analytical Algorithm (AAA), Acuros XB (AXB), Monte Carlo (MC) and Collapsed Cone Volume (CCV).

Method: This study was carried out using a CIRS Model 002LFC IMRT Thorax Phantom customized with a water-equivalent heterogeneity inside the lung.

Design of experiments in medical physics: Application to the AAA beam model validation.

Purpose: The purpose of this study is to evaluate the usefulness of the design of experiments in the analysis of multiparametric problems related to the quality assurance in radiotherapy. The main motivation is to use this statistical method to optimize the quality assurance processes in the validation of beam models.

Method: Considering the Varian Eclipse system, eight parameters with several levels were selected: energy, MLC, depth, X, Y and Y jaw dimensions, wedge and wedge jaw.

Conditionality and risk for the pedestrian: modelling with the Bayesian networks.

The conditional script questionnaire (CSQ) makes possible to study the conditions under which drivers find it legitimate to transgress the Highway Code. In this paper, we propose to analyse conditional respect towards the pedestrian with a new methodology based on Bayesian networks (BN). This methodology is designed to give a useful decision support tool for the analyst.