  A radio-guided surgery technique exploiting $\beta^-$ emitters is under
development. It aims at a higher target-to-background activity ratio implying
both a smaller radiopharmaceutical activity and the possibility of extending
the technique to cases with a large uptake of surrounding healthy organs. Such
technique requires a dedicated intraoperative probe detecting $\beta^-$
radiation. A first prototype has been developed relying on the low density and
high light yield of the diphenylbutadiene doped para-therphenyl organic
scintillator. The scintillation light produced in a cylindrical crystal, 5 mm
in diameter and 3 mm in height, is guided to a photo-multiplier tube by optical
fibres. The custom readout electronics is designed to optimize its usage in
terms of feedback to the surgeon, portability and remote monitoring of the
signal. Tests show that with a radiotracer activity comparable to those
administered for diagnostic purposes the developed probe can detect a 0.1 ml
cancerous residual of meningioma in a few seconds.
