European Organization for Nuclear Research

Agence Nationale De Valorisation De La Recherche (anvar)

Ebamed Sa

Fabio Sauli

Georges Charpak

Adriano Garonna

Armando Policarpo

N'Guyen N Hoan

A medical imaging tool is described, capable of providing in real time 2-D images of the prompt gamma fields released during patient treatment. Owing to its millimetre position accuracy, the instrument is particularly suited for applications where a precise determination of the end-of-range (Bragg peak) of the beam is of paramount importance, as in cancerous and non-cancerous targets for treatment with ion beams and for the treatment of atrial fibrillation. With its unique dual-layer conception in coincidence, the instrument has high rejection ability against false neutron-generated counts, the principal source of background noise for in-beam dose monitoring. It can also provide a coarse measurement of the gamma incidence angle, permitting a correction of the parallax error, main source of dispersion for large area detectors employing collimators.

Prompt gamma monitor for hadron therapy

A parallax-free X-ray imager in which a parallel X-ray beam is directed to a crystal for illuminating an entrance window is formed in a vessel filled with an ionizing gas in which primary electrons are generated. A spherical conversion volume chamber is formed by the entrance window and a first and a second parallel electrodes are adapted to generate electrical equipotential surfaces of spherical shape allowing the primary electrons to drift along corresponding radial field lines. A third electrode parallel with the second electrode is provided so as to form a gas electron multiplier structure consisting of a matrix of electric field condensing areas which are adapted to operate as an amplifier of the primary electrons through an avalanche phenomenon. A signal readout electrode is provided to allow a bi-dimensional readout in the absence of parallax readout phenomenon.

Planispherical parallax-free X-ray imager based on the gas electron multiplier

A radiation detector in which primary electrons are released into a gas by ionizing radiations and drifted through an electric field to a collecting electrode for detection. It further includes a gas electron multiplier formed by one or several matrices of electric field condensing areas which are distributed within a solid surface perpendicular to the electric field. Each electric field condensing area consists of a tiny hole passing through the solid surface that forms a dipole adapted to produce a local electric field amplitude enhancement proper to generate an electron avalanche from one primary electron. The gas electron multiplier operates thus as an amplifier or a preamplifier within a host radiation detector.

Radiation detector of very high performance

A gas scintillation proportional counter, with a photosensitive layer, is coupled, through a UV transparent window, to a multi-anode proportional chamber filled with a gas mixture (for instance an argon triethylamine-methane mixture) having a large quantum efficiency for the UV photons. When detecting incident photons, there is obtained the good efficency of photosensitive layers and the satisfactory two-dimensional coordinate localization of multiwire proportional chambers.

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Geneva, Switzerland

Fabio Sauli