Integration of CT/PET images for the optimization of radiotherapy planning

A procedure is presented, based on the combined use of two different tomographic imaging modalities (PET and CT), aimed at the optimization of radiotherapy planning. The combined use of functional PET and anatomical CT studies allows a better definition of the tumour mass with respect to the conventional CT based approach. The proposed procedure consists in: a) spatial registration of CT and PET studies; b) contour drawing based on the combined observation of PET and CT. The set of contours thus obtained, defining optimized volumes of interest for radiotherapy, can be exported to the treatment planning system for designing the radiation beam geometry. The accuracy of the image registration was evaluated by phantom studies and found to be less than 2 pixels in plane and less than slice thickness axially, with respect to CT. The application of the procedure to the case of a patient affected by pancreatic tumour is presented, showing how the treatment planning can be improved by multimodal CT/PET information.