PET Evaluation of Response After 1 Course of Chemotherapy as Predictor of Treatment Outcome.

Study hypothesis : early decrease in fdg-pet measured SUV max after 1 cycle of chemotherapy can accurately predict response of chemotherapy as assessed by conventional radiology after 3 cycles of chemotherapy.
FDG-PET imaging will be done at J0 and J14 of a new line of chemotherapy treatment in metastatic colorectal cancer.
SUV max will be recorded and delta SUVmax will be compared to the results of conventional radiological evaluation after 3 courses of chemotherapy. Results will also be compared to the time to disease progression.