PET online for protons and ions

Positron emission tomography (PET) is currently the only technically feasible method for invivo, non-invasive monitoring of the precision of the dose delivery in highly conformal ion therapy. Online (in-situ) implementation offers the attractive advantages to detect the significant contribution from short-lived emitters e.g. 15O, reduce image degradation due to perfusion and acquire data in treatment position. To date, clinical applications of online PET have been limited to the concluded trial of range verification with radioactive isotopes prior to stable ion irradiation at Lawrence Berkeley Laboratory (LBL), USA, and the ongoing routine monitoring of stable carbon ion irradiation at the Gesellschaft für Schwerionenforschung Darmstadt (GSI), Germany. The rapidly growing number of proton therapy facilities is stimulating the research on the applicability of PET monitoring to protons. However, due to instrumentation restrictions and costs, most of the former and ongoing studies were carried out offline at remote, conventional PET scanners. Extensive in-beam phantom experiments with proton beams were recently finished at GSI using the available dedicated, unique online tomographic positron camera. The main results, providing novel insight and supporting the applicability and usefulness of online PET for proton therapy monitoring, will be reported.