Journal Article Induced radioactivity of a GSO scintillator by secondary fragments in carbon ion therapy and its effects on in-beam OpenPET imaging

Hirano, Yoshiyuki  ,  Nitta, Munetaka  ,  Nishikido, Fumihiko  ,  Yoshida, Eiji  ,  Inadama, Naoko  ,  Yamaya, Taiga

61 ( 13 )  , pp.4870 - 4889 , 2016-07 , IOPscience
The accumulation of induced radioactivity within in-beam PET scannerscintillators is of concern for its long-term clinical usage in particle therapy.To estimate the effects on OpenPET which we are developing for in-beam PETbased on GSOZ (Zi doped Gd2SiO5), we measured the induced radioactivityof GSO activated by secondary fragments in a water phantom irradiation by a12C beam with an energy of 290 MeV u−1. Radioisotopes of Na, Ce, Eu, Gd,Nd, Pm and Tb including positron emitters were observed in the gamma rayspectra of the activated GSO with a high purity Ge detector and their absoluteradioactivities were calculated. We used the Monte Carlo simulation platform,Geant4 in which the observed radioactivity was assigned to the scintillatorsof a precisely reproduced OpenPET and the single and coincidence ratesimmediately after one treatment and after one-year usage were estimated forthe most severe conditions. Comparing the highest coincidence rate originatingfrom the activated scintillators (background) and the expected coincidencerate from an imaging object (signal), we determined the expected signal-tonoiseratio to be more than 7 within 3 min and more than 10 within 1 min fromthe scan start time. We concluded the effects of scintillator activation and theiraccumulation on the OpenPET imaging were small and clinical long-termusage of the OpenPET was feasible.Keywords: in-beam PET, GSO scintillator, particle therapy, openPET,induced radioactivity, secondary fragments(Some figures may appear in colour only in the online journal)

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