GaN diode array for proton monitoring and imaging – MATRIX

The MATRIX project aims at improving the proton therapy for cancer treatment by developing new detectors which will increase the control on the irradiation dose and make treatments faster and more reliable. Proton irradiation is the most accurate therapy against cancer as it allows irradiating tumors with high doses without affecting the healthy tissues nearby (especially downstream). Proton therapy is currently very actively developing, both in terms of number of proton centers in the world (currently around 90 with a few new units every year) and in terms of protocols and equipment: pencil beam scanning becomes popular, beam monitoring before and during treatments improves, proton imaging emerges…There is a need for proton detectors with higher sensitivity, dynamic range, spatial resolution, which allow performing quality assurance faster, better, cheaper. Ultimately, all these improvement will allow treating more patients, with better protocols and save more lives.
High energy protons (from 65 to 230 MeV) can be detected by various techniques, from ionization chambers to semiconductor devices. Semiconductors allow fabricating detector arrays with the best spatial resolution and sensitivity. They are however prone to degradation under high energy particle bombardment. In particular, silicon devices, which are the most popular and developed ones for many applications, are very fragile under irradiation, and degrade with the cumulated dose. We propose to use another semiconductor, which is about 10 times more resistant to irradiation: gallium nitride, a widely spread semiconductor used in LEDs for solid state lighting, which means that the detector can be produced at low cost. The detectors will be coupled to silicon electronics, which allows reading and processing the data. The Si electronics will be out of the irradiation field so that it will not suffer degradation. Hence, the project targets a high performance system, by combining the best two materials in their respective field. A 2-dimensional imaging array, 5 cm x 5 cm and a 200 µm resolution will be fabricated, which is way beyond any existing similar device in the world.

CRHEA-CNRS (Sophia Antipolis, France) brings its internationally recognized expertise in the growth of GaN layers, and the fabrication of GaN based devices. The Ruhr-University of Bochum, Germany, brings its long standing expertise in irradiation and implantation, and in electronic properties in materials. They will also operate the hybrid Si-GaN imaging system. Tests under proton irradiation will be performed both in France (Lacassagne center, Nice) and in Germany (West German Proton Therapy Center, Essen). Proton beam measurements will be performed in various and complementary configurations (energy, beam size, intensity) in both centers, so that this German-French collaboration will allow us to cover most quality assurance protocols used in proton therapy centers.