In-beam PET measurement of 7Li3+ irradiation induced beta+-activity

At present positron emission tomography (PET) is the only feasible method of an in situ and non-invasive monitoring of patient irradiation with ions. At the experimental carbon ion treatment facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt an in-beam PET scanner has been integrated into the treatment site and lead to a considerable quality improvement of the therapy. Thus, it is highly desirable to extend in-beam PET also to other therapeutic relevant ions which requires an extensive knowledge on the spatial distribution of generated positron emitters. Therefore, by means of the in-beam PET scanner at GSI the beta+-activity induced by 7Li3+ ions has been investigated for the first time. Targets of PMMA, water, graphite and polyethylene were irradiated with monoenergetic, pencil-like beams of 7Li3+ with energies between 129.1 AMeV and 205.3 AMeV and intensities ranging from 3.0 e7 to 1.9 e8 ions s-1. This paper presents the measured beta+-activity profiles as well as depth dependent thick target yields which have been deduced from the experimental data. The beta+-activity induced by 7Li ions was found to be a factor of 1.9 higher than the one induced by 12C ions at the same physical dose and particle range.