Seminar: Positron Emission Tomography for real-time verification during particle beam radiotherapy

In comparison to photon radiotherapy, particle beam radiotherapy (mostly protons and carbon ions are used) results in a lower radiation dose to normal tissue, reducing long-term complications and increasing the quality of life of patients. However, the dose distribution delivered during particle therapy is quite sensitive to anatomical changes in the patient, particle range uncertainties and patient setup errors. Because of this, several techniques for in vivo dose delivery verification have and are being developed. The most investigated method is positron emission tomography (PET) of the positron emitters that are created by the particles via nuclear reactions in the patient. The PET signal is obviously delayed by the radioactive decay half-life. For most positron emitters this precludes real-time feedback and leaves room for biological washout.

I will report on investigations towards real-time verification using PET during proton, helium ion and heavy ion therapy. At the University Medical Center Groningen, we are investigating imaging of 12N, with a half-life of just 11 ms, produced by the proton or helium beam in the patient. I will report on recent proof-of-principle demonstrations of the range accuracy in homogeneous targets, and discuss our present research to establish the clinical relevance on the basis of irradiations of an anthropomorphic head phantom. Treatment with positron-emitting radioactive heavy ions gives a much stronger PET signal which is more closely correlated to the Bragg peak compared to treatment with stable heavy ions. Within the BARB project at the GSI Helmholtzzentrum für Schwerionenforschung, we have investigated the precision with which the range of 10,11C and 14,15O can be measured using PET. The design and outcome of these experiments will be discussed.