APPLICATION OF POSITRON EMISSION TOMOGRAPHY IN COLORECTAL-CARCINOMA

New diagnostic methods like the positron emission tomography (PET) pro vide functional information about tumors and metastases. Tumor perfusi on can be quantitatively evaluated with the use of radiolabeled tracer s. Furthermore, quantitative data on the tumor metabolism are obtained with metabolically active radio-pharmaceuticals. PET studies with F-1 8-deoxyglucose and other tracers like amino acids can help to achieve and early diagnosis of tumor recurrence. While the sensitivity of PET is high for recurrent colorectal tumors (29/30 true positive), false p ositive results may be obtained in patients with inflammatory reaction s. Therefore, a quantitative evaluation of the data is mandatory, and the results must be interpreted in combination with preexisting clinic al data. F-18-labeled fluorouracil (FU) can be used to obtain quantita tive data on kinetics and therapeutic effects. The comparison of syste mic and regional tracer injection showed that perfusion and FU transpo rt into the tumor cells can ne independent parameters. The outcome of chemotherapy can be predicted using F-18-labeled FU and PET prior to t he first chemotherapeutic cycle. A correlation of 0.86 was noted for t he F-18-FU accumulation and the tumor growth rate during chemotherapy. Studies in primary colorectal tumors treated with regional FU infusio n demonstrated a correlation of the FU accumulation with tumor blood f low and metabolism. PET can be used in these patients to select the on es who are most likely to respond to therapy. Since the number of radi olabeled cytostatic drugs is limited at present, the development of ne w radiolabeled cytostatic agents is the major aim of a combined workin g group from the EORTC and the EEC Programme on PET.