EP-1279: Non coplanar positioning evaluation on stereotactic cranial treatments with a TrueBeam On Board Imaging.

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Design of a 10 nm electron collector for a track-nanodosimetric counter

Recently we have developed a track-nanodosimetric counter, which is a gas detector that measures the distributions of electrons induced by a charged particle in nanometric volumes of tissue equivalent matter, positioned at different distances from the track. Sites equivalent to 20 and 24 nm were defined by means of an electron collector, which is a system of electrodes enclosing an almost wall-less cylindrical volume. In this paper, we present the design of a new electron collector that is able to simulate a volume as small as 10 nm in diameter

Erratum à « Radiothérapie des cancers du larynx » [Cancer Radiother. 26 (2022) 206–12]

International audienc

Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy

Purpose: Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medical linacs in radiotherapy. Methods: The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. Results: Definitions for dose profile parameters are suggested starting from the renormalization of the with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of "unflatness" and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. Conclusions: Ideas for quality controls used in establishing a quality assurance program when introducing FFF, beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4754799

A detector for track-nanodosimetry

In this paper, we describe a gas counter able to measure electron cluster distributions in nanometric sized sites. We designed a system of electrodes that is able to collect electrons from a nanometric wall-less sensitive volume and to transfer them to a counter that detects single electrons. Measurements of electron collection efficiency in propane gas confirm that we successfully collected electrons from a wall-less sensitive volume, of about 20 mm width, with an average efficiency of more than 20%

Study of non-equilibrium electron avalanches, application to proportional counters

The process of gas multiplication in uniform and non-uniform electric fields is analyzed on the basis of a numerical solution of the Boltzmann equation, Monte Carlo simulations and experimental gas gain measurements. We give a brief Boltzman equation description of gas multiplication that points out the different behaviour of the ionization coefficient in uniform and non-uniform electric fields. We introduce the concept of quasi equilibrium as an extension of the equilibrium formulation to non-uniform electric fields. Monte Carlo results for the reduced ionization coefficient and reduced gas gain for methane and propane in cylindrical geometry are presented illustrating their simultaneous dependence on the reduced voltage K and the reduced electric field S. Gas gain measurements for a propane-tissue-equivalent gas mixture are presented, which demonstrate this dependence