The aim of this study is to introduce tools to improve the security of each IMRT patient treatment by determining action levels for the dose delivery process. To achieve this, the patient-specific quality control results performed with an ionization chamber-and which characterize the dose delivery process-have been retrospectively analyzed using a method borrowed from industry: Statistical process control ͑SPC͒. The latter consisted in fulfilling four principal well-structured steps. The authors first quantified the short term variability of ionization chamber measurements regarding the clinical tolerances used in the cancer center ͑Ϯ4% of deviation between the calculated and measured doses͒ by calculating a control process capability ͑C pc ͒ index. The C pc index was found superior to 4, which implies that the observed variability of the dose delivery process is not biased by the short term variability of the measurement. Then, the authors demonstrated using a normality test that the quality control results could be approximated by a normal distribution with two parameters ͑mean and standard deviation͒. Finally, the authors used two complementary tools-control charts and performance indices-to thoroughly analyze the IMRT dose delivery process. Control charts aim at monitoring the process over time using statistical control limits to distinguish random ͑natural͒ variations from significant changes in the process, whereas performance indices aim at quantifying the ability of the process to produce data that are within the clinical tolerances, at a precise moment. The authors retrospectively showed that the analysis of three selected control charts ͑individual value, moving-range, and EWMA control charts͒ allowed efficient drift detection of the dose delivery process for prostate and head-and-neck treatments before the quality controls were outside the clinical tolerances. Therefore, when analyzed in real time, during quality controls, they should improve the security of treatments. They also showed that the dose delivery processes in the cancer center were in control for prostate and head-and-neck treatments. In parallel, long term process performance indices ͑P p , P pk , and P pm ͒ have been analyzed. Their analysis helped defining which actions should be undertaken in order to improve the performance of the process. The prostate dose delivery process has been shown statistically capable ͑0.08% of the results is expected to be outside the clinical tolerances͒ contrary to the head-and-neck dose delivery process ͑5.76% of the results are expected to be outside the clinical tolerances͒.

This study presents a method aimed at creating radiotherapy (RT) patient-adjustable whole-body phantoms to permit retrospective and prospective peripheral dose evaluations for enhanced patient radioprotection. Our strategy involves virtual whole-body patient models (WBPM) in different RT treatment positions for both genders and for different age groups. It includes a software tool designed to match the anatomy of the phantoms with the anatomy of the actual patients, based on the quality of patient data available. The procedure for adjusting a WBPM to patient morphology includes typical dimensions available in basic auxological tables for the French population. Adjustment is semi-automatic. Because of the complexity of the human anatomy, skilled personnel are required to validate changes made in the phantom anatomy. This research is part of a global project aimed at proposing appropriate methods and software tools capable of reconstituting the anatomy and dose evaluations in the entire body of RT patients in an adapted treatment planning system (TPS). The graphic user interface is that of a TPS adapted to obtain a comfortable working process. Such WBPM have been used to supplement patient therapy planning images, usually restricted to regions involved in treatment. Here we report, as an example, the case of a patient treated for prostate cancer whose therapy planning images were complemented by an anatomy model. Although present results are preliminary and our research is ongoing, they appear encouraging, since such patient-adjusted phantoms are crucial in the optimization of radiation protection of patients and for follow-up studies.

Several methods for electron number density (Ne) determination in a SF6 arc plasma are successively described: two-wave laser interferometry, Stark broadening of neutral sulphur lines, an original method derived from Stark broadening of a sulphur triplet, the recombination continuum and the derivation of Ne from temperature measurement. The results are in good agreement; they show the existence of departures from LTE due to a demixing effect.

Deals with an experimental and theoretical study of the difference between the electron temperature Te and the gas temperature Tg in a stationary cylindrical argon plasma. The experimental method is based on the measurement of a line coefficient, during the first microseconds of plasma decay, which presents a jump due to the equalisation of temperatures. A theoretical model with rate equations and the electron energy balance has been developed. The comparison between experimental and theoretical values of the difference (Te-Tg) has been carried out for several current intensities and radial positions. The agreement is good for an arc with a 6 mm diameter. For a 4 mm diameter the computed values are less precise than the experimental ones because of the inaccuracy of diffusion terms which play an important part in the computation of (Te-Tg).

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