Charged hadron tumour therapy monitoring by means of PET

Positron emission tomography (PET) imaging of radioactivity distributions induced by therapeutic irradiation is at present the only feasible method for an in situ and non-invasive monitoring of radiooncology treatments with ion beams. Therefore, at the experimental carbon ion therapy facility at the Gesellschaft für Schwerionenforschung Darmstadt, Germany (GSI) a PET scanner has been integrated into the treatment site for quality assurance monitoring simultaneously to the therapeutic irradiation. Although the device has been assembled from components of positron emission tomographs developed for nuclear medicine applications, substantial modifications had to be made for meeting the requirements of ion therapy monitoring. These changes regard the geometrical detector configuration as well as the data acquisition and processing. Since 1997 this technique has been applied to monitor the fractionated irradiation of more than 180 patients predominantly suffering from tumours in the head and neck region. It could be demonstrated that this new PET technique is capable of assessing parameters being relevant for quality assurance of carbon ion therapy, i.e. the particle range in tissue, the position of the irradiated volume with respect to anatomical landmarks and local deviations between the planned and the applied dose distributions.