In comparison to photon radiotherapy, proton beam radiotherapy generally 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 proton therapy is quit e sensitive to anatomical changes in the patient, proton range uncertainties and treatment errors. Because of this, several techniques for in-vivo dose delivery verification have and are being developed. We are investigating positron emission tomography (PET) of 12N produced by the proton beam in the patient. The very short half-life of 12N (11 ms) enables quasi real time feedback and precludes biological washout. I will report on recent proof-of-principle demonstrations, showing measurements of the range of 12N production by 150 MeV protons in PMMA targets with a precision of 2.7 resp. 0.9 mm for 10^8 resp. 10^9 protons. These results will be extrapolated to an optimized clinical PET setup. Finally, the roadmap towards clinical implementation will be outlined.
Peter Thirolf (LMU) / Norbert Kaiser (TUM)