FDG-positron emission tomography (PET) as an indicator of response to chemotherapy : a study of patients with upper gastrointestinal cancer and metastic colorectal liver cancer
Background. FDG-PET detects metabolic activity within tumour tissue and may have the ability to detect response in patients receiving chemotherapy. Materials and Methods. Patients with upper GI cancer had FDG-PET imaging performed at the time of diagnosis and on completion of planned treatment in those receiving chemotherapy. Scans were quantified using tumour/liver ratios (TLR) and standardised uptake values (SUV) in all patients and by the calculation of the tumour uptake constant of FDG (K value) using dynamic imaging. For comparative purposes all patients had CT scans, dysphagia scores and weight recordings. Patients with metastatic colorectal liver cancer had FDG-PET pre and post 1 cycle of 5FU/folinic acid. CT scans and Carcino Embryonic Antigen (CEA) levels were used for comparison of response. Survival figures were available for all patients. Results. Forty patients were recruited for the gastrointestinal study including 17 patients receiving chemotherapy. 39 of 40 tumours were successfully imaged. FDG uptake did not correlate with stage T or N stage of disease. A wide range of changes in FDG activity were seen in tumours pre and post chemotherapy ranging from a 15% increase in activity to a 100% reduction. The highest correlation between quantitative method existed between TLR and K value was 0.8967 (P<0.001, 2-tailed). There was general agreement between PET, CT and clinical evidence of response. Thirty-four liver metastases in 13 patients were assessed for evidence of response. A change in tumour/liver ratio of less than 20% was seen in 25 of 34 lesions. At 2 weeks post therapy the changes in FDG uptake was generally small and non-uniform. Conclusions. FGD- PET is useful in the detection of upper GI tumours and may have a role to play in the identification of tumour response to chemotherapy.