Positron Emission Tomography for real-time verification during proton therapy

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 quite 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 10⁸ resp. 10⁹ protons. These results will be extrapolated to an optimized clinical PET setup. Finally, the roadmap towards clinical implementation will be outlined.