Role of F18-FDG PET for Monitoring of Radiochemotherapy – Estimation of Detectable Number of Tumour Cells

Background: FDG-PET has been proven to be useful for the diagnosis of pancreatic cancer. However, no quantitative data exist concerning its sensitivity for treatment monitoring or early diagnosis. Case Report: We report on a 61-year-old patient with locally advanced cancer of the pancreas head who received sequential radiochemotherapy including gemcitabine and 5-FU/FA. Under this regimen, MR and CT showed a partial remission with a residual mass which seemed to allow surgical treatment for this patient. A pre-operative FDG-PETScan displayed a count rate close to the detection limit of vital residual tumour. An R0 resection was performed successfully. However, histopathology revealed residual tumour at the core of the resected mass that had gone undetected by all imaging modalities. Conclusion: The number of vital tumour cells within this specimen was estimated to be 10 6 –10 7 . The detection threshold for FDG-PET in pancreatic carcinoma appears to be within this range.