A new spectrometer to monitor a proton beam for therapy at cyclone (Louvain-la-Neuve)

The energy loss of high LET charged particles in tissue increases in depth and exhibits the well known sharp Bragg peak at the end of the particle trajectory. The use of this physical characteristic for therapeutic applications implies the adaptation of the Bragg peak to the extended target volume. Current techniques use space and energy modulation of the primary monoenergetic beam. In the case of the 90 MeV proton beam produced by CYCLONE at Louvain-la-Neuve (Belgium), it is considered to modulate the beam in space by beam transport elements and to modulate the beam in energy by variable absorbers. This contribution presents a spectrometer to monitor the modulated beam. It consists of 4 plastic scintillators with a continuously variable perspex absorber. The spectrometer gives three types of information: 1) The range distribution of the proton beam in a given material: logical information. 2) The energy loss as a function of penetration length: analogical information. 3) The proton energy spectrum after modulation by a NaI detector: analogical information. The actual performance of the spectrometer with respect to the 3 different types of information has been investigated for 65 MeV protons