Watch Dog detector for beam diagnostic in hadrontherapy application

The "Watch Dog" is a beam monitor designed for medical accelerators, that will be installed at the end of the CNAO (Centro Nazionale di Adroterapia Oncologica) extraction lines. Its main goal is to achieve a real time monitoring of the beam position during patient treatments; the system can generate an interlock signal in case the measured quantity is out of the nominal range. In this paper the Watch Dog is described, and preliminary tests are presented.