Investigation of alternative imaging methods to improve accuracy in cancer therapy with carbon ions

The interest in carbon therapy for cancer treatment has been growing. However, in order to take full advantage of their depth-dose curve, precise knowledge of their range and patient interfaces is necessary. Range uncertainties in carbon therapy are significant due to the current method to determine the range, which uses X-ray CT and a calibration curve, and due to patient variations. The purpose of this dissertation was to find possible solutions to decrease range uncertainties. The first method consisted in optimizing the elemental ionization values in the calculation of the relative stopping powers in order to obtain a better estimation of the calibration curve. The second method involved a phenomenological approach which predicted carbon paths trajectories better than using straight path trajectories (root mean square error was reduced by 50 %). The third method, used multiple Bragg peak detection in order to obtain knowledge about the tumor edge position in a high contrast medium. The method avoided irradiation of multiple angles/positions and provided 1mm accuracy in the determination of the tumor edge. Finally, the forth and last method proposed the use of charged particle (protons, carbons and heliums) radiography combined with X-ray CT to obtain a patient-specific calibration curve to be used for carbon range calculations. The obtained results were extremely promising with maximum range errors of 1.5mm for helium radiography. These results suggest that helium radiography might be the method of choice for future carbon and proton treatment planning. The results derived in the different chapters of this dissertation show that carbon therapy accuracy can be increased with respect to current clinical practice.