18F-FLT-PET for detection of rectal cancer

This pilot study was undertaken to examine the ability of (18)F-3'-fluoro-3'-deoxy-l-thymidine positron emission tomography ((18)F-FLT-PET)to detect rectal cancer, to identify pathologic lymph nodes and to determine the accuracy of tumour length estimation in comparison with computer tomography (CT).

Nine patients with biopsy proven rectal cancer underwent CT and (18)F-FLT-PET scanning prior to short-term pre-operative radiotherapy (5×5Gy). Within 10 days after the start of radiotherapy a surgical resection was performed. Tumour lengths and regional lymph node visualisation on both imaging modalities were compared with pathology findings.

All tumours were visible on CT. (18)F-FLT-PET visualised 7 out of 9 tumours (78%). The pathology-based tumours lengths correlated better with CT as compared to FLT-PET(r=0.91, p<0.01). (18)F-FLT-PET was not able to visualise pathologic lymph nodes. However, CT identified all patients with pathologic lymph nodes.

Primary rectal cancer can be visualised by (18)F-FLT-PET in the majority of cases but not in all. However, (18)F-FLT-PET was not able to identify pathologic lymph nodes. Therefore, we conclude that (18)F-FLT-PET has limited value for the detection of pathologic lymph nodes and tumour delineation in rectal cancer.