Real-time positron emission tomography for range verification of particle radiotherapy

Owing to the superior ability to deliver the prescribed radiation dose to cancer tissue with a reduced dose to surrounding healthy tissues, there has been a sustained increase in cancer radiotherapy with charged particles, such as protons, helium and carbon ions. Achieving such superior dose delivery is, however, nontrivial as the dose distribution by charged particles is sensitive to uncertainties in range prediction, patient setup errors and changes in patient anatomy. This thesis investigates a technique to provide feedback on the particle range, based on the imaging of photons, emitted via the radioactive decay of positron emitting nuclides produced through nuclear reactions. Retrieving such feedback on a short time scale provides a trigger for corrective actions such as online treatment adaptation. Experiments on the production of short-lived positron emitters during irradiation with helium ions as reported in chapter 3 and the PET imaging of these nuclides during irradiations with helium ions (chapter 4) and protons (chapter 5) were performed. It was observed that the short-lived positron emitter nitrogen-12 (half-life = 11 ms), previously observed during irradiation with protons, is also produced during irradiation of a tissue surrogate, PMMA, with helium ions. Extrapolating the experimental results to an optimized implementation of the method, feedback on the particle range at a time-scale of about 50 ms into an irradiation with 109 protons and 4.0 × 108 helium-4 ions with a precision (1σ) of 0.5 mm and 0.9 mm is predicted. The next steps towards clinical implementation are detailed in chapter 6