Results of a 20 minutes decay measurement of a patient irradiation by the in-beam PET scanner

F. Fiedler1, D. Möckel1, K. Parodi2, J. Pawelke1, F. Pönisch1,3, M. Priegnitz1, G. Shakirin1, and W. Enghardt1,3 1FZD, Dresden, Germany; 2HIT, Heidelberg, Germany; 3OncoRay, TU Dresden, Germany Introduction Over the last 10 years, the unique installation of an inbeam PET-scanner at the heavy-ion treatment facility at GSI [1] has demonstrated the benefit of in-beam PET measurements. Additional heavy ion therapy facilities are under construction. Monitoring the irradiation is highly desirable especially for heavy-ion beams, because the beam has the potential to cause excessive damage in the healthy tissue surrounding the tumor. The evaluation of in-beam PET results is based on a comparison between measurement and simulation. Even if all the physical processes of creating and detecting positron emitters are correctly modeled, deviations between measured and simulated βemitter distribution will occur. The predominant reason for that is the blurring as well as the reduction of measured activity via washout. To get realistic estimation of the quantity of washout a decay measurement of 20 minutes was performed over 20 patient treatments, referred to as “fractions”. Methods and Results The listmode data were taken by the data acquisition system of the in-beam PET camera [1], and spatial subsets were analyzed. We classified the lines of response (LOR) depending on the Hounsfield unit (HU) on the basis of the patient’s planning computer tomogram (CT). For each LOR intersecting the irradiated volume, the mean HU (HU) and its standard deviation were calculated. The LOR were combined as given in table 1. Since the main positron emitters are well known we fitted the decay curves according to