Can an FDG-PET/CT predict tumor clearance of the mesorectal fascia after preoperative chemoradiation of locally advanced rectal cancer?

BACKGROUND AND PURPOSE

More effective preoperative treatment in locally advanced rectal cancer gives rise to a more individualized, conservative surgical treatment strategy. This, however, requires accurate information on tumor response after chemoradiation (CRT). So far, MRI and CT have failed to provide such information. Therefore, the value of a combined FDG-PET/CT in predicting tumor clearance of the mesorectal fascia (MRF) was determined.

PATIENTS AND METHODS

20 rectal cancer patients with MRF tumor invasion underwent preoperative PET/CT before and on average 6.3 weeks after CRT. The SUV(max)(maximal standard uptake value) on sequential PET/CT and the shortest distance between the outlined tumor volume and the MRF measured by using autocontouring software on post-CRT PET/CT were registered. The surgical specimen was evaluated for tumor clearance of the MRF and the tumor regression grade (TRG).

RESULTS

The TRG significantly corresponded with the SUV(max)changes induced by CRT (p = 0.025), and showed a trend with the post-CRT SUV(max)(TRG 1-2 vs. TRG 3-5: SUV(max)= 3.0 vs. 5.0; p = 0.06). However, the pathologically verified tumor clearance of the MRF was not correlated with any of the tested SUV parameters nor with the shortest distance between the residual tumor and the MRF.

CONCLUSION

Post-CRT PET/CT is not a useful tool for evaluating anatomic tumor changes and, therefore, not accurate in predicting tumor clearance of the MRF. However, it might be a useful tool in predicting pathologic tumor response after CRT.