Modern multimodal neuroimaging for radiosurgery: the example of PET scan integration

Radiosurgery relies critically on medical imaging modalities. Leksell Gamma Knife (LGK) radiosurgery presents the highest requirements in terms of imaging accuracy as the treatment is applied in a single high-dose session with no other spatial control than medical imaging. The advent of new imaging modalities opens challenges for LGK planning strategies. The integration of stereotactic PET in LGK represents an example of such application of modern multimodality imaging in radiosurgery. Our experience consists of 80 patients treated with the combination of MR/CT and PET guidance. In order to analyze the specific contribution of PET findings, we developed a classification reflecting the strategy used to define the target volume. When combining PET and MR information, 102 target volumes were defined, because some patients presented with multiple lesions or multifocal tumor areas. Abnormal PET uptake was found in 86% of the lesions, and this information altered significantly the MR-defined tumor in 73%. In conclusion, integration of PET in radiosurgery provides additional information opening new perspectives for the treatment of brain tumors. The use of a standardized classification allows to assess the relative role of PET. A similar approach could be useful and may serve as a template for the evaluation of the integration of other new imaging modalities in radiosurgery.