Study of the time and space distribution of beta(+) emitters from 80 MeV/u carbon ion beam irradiation on PMMA

Proton and carbon ion therapy is an emerging technique used for the treatment of solid cancers. The monitoring of the dose delivered during such treatments and the on-line knowledge of the Bragg peak position is still a matter of research. A possible technique exploits the collinear 511 key photons produced by positrons annihilation from beta(+) emitters created by the beam. This paper reports rate measurements of the 511 keV photons emitted after the interactions of a 80 MeV/u fully stripped carbon ion beam at the Laboratori Nazionali del Sud (LNS) of INFN, with a poly-methyl methacrylate target. The time evolution of the beta(+) rate was parametrized and the dominance of C-11 emitters over the other species (N-13, O-15, O-14) was observed, measuring the fraction of carbon ions activating beta(+) emitters to be (10.3 +/- 0.7) x 10(-3). The average depth in the PMMA of the positron annihilation from beta(+) emitters was also measured, D beta+ = 5.3 +/- 1.1 mm, to be compared to the expected Bragg peak depth D-Bragg = 11.0 +/- 0.5 mm obtained from simulations. (C) 2012 Elsevier B.V. All rights reserved.