Fluorine-18 fluoro-2-deoxyglucose positron emission tomography in recurrent rectal cancer: relation to tumour size and cellularity

The aim of this study was to assess the value of fluorine-18 fluoro-2-deoxyglucose (FDG) positron emission tomography in patients with recurrent rectal cancer, in relation to tumour size and cellularity. Thirty-seven patients (21 mean and 16 women; mean age, 55.4±9.58 years) with suspected recurrence of rectal cancer were studied. FDG uptake was quantified by the differential absorption ratio (DAR). In 29 patients magnetic resonance imaging was also performed. To evaluate the signal intensity of the lesion, the lesion to muscle signal intensity ratios (SIR) were calculated on T2-weighted images. In seven patients who received surgical treatment the DAR and SIR were compared with the tumour cellularity. All 32 patients with confirmed recurrence showed increased FDG accumulation in the mass (DAR=4.57±1.89) in comparison with low FDG accumulation in five patients with scar (DAR=1.17±0.43). There was a significant correlation (r=0.661,P<0.001) between the DAR and the tumour diameter. There was no correlation between the DAR and SIR, whereas there was a significant correlation (r=0.565,P<0.01) between the DAR corrected using count recovery coefficient (DAR^*) and SIR. In the histopathological findings there was a tendency for the DAR^* and SIR to correlate with tumour cellularity. It is concluded that the DAR of recurrent rectal cancer should be evaluated taking into consideration the tumour size and cellularity.