ON LINE MEASUREMENTS OF PROTON FLUX BY HIGH-ENERGY BACKSCATTERING SPECTROSCOPY

Proton radiotherapy is typically based on 70-200 MeV protons to irradi ate limited volumes of diseased biological tissues. The absorbed dose is determined by the amount of proton energy released in the target i. e. the proton flux, the stopping power and the irradiation time. In th is paper an experimental method is reported to make an on line measure ment of proton flux, energy and beam stability. The facility is constr ucted at the 15 MV Tandem accelerator of the INFN-LNS in Catania (Ital y) where preliminary studies are in progress. Investigations are perfo rmed at a proton energy of about 30 MeV, lower with respect to the the rapeutic ones: but useful to simulate the clinical beams and to discov er problems arising from their use. With the aim to use 70 MeV protons delivered by the LNS superconducting cyclotron for eye therapy, a gol d scatterer is used to broaden the beam and to get a good uniformity o ver some centimeters in air. The scatterer is also used to produce the backscattered protons component which is detected with a thick silico n surface barrier detector. The detected yield is proportional to the beam flux and gives information about the beam energy and the current stability. (C) 1997 Published by Elsevier Science B.V.