[Contrast media kinetic in multi-slice helical CT cannot detect rectal cancer recurrence with certainty]

Evaluation of different parameters of contrast media enhancement for the differentiation between scar tissue and local recurrence of rectal cancer.

We included 83 patients after operation and radiotherapy of rectal cancer. In total, 20 local recurrences were diagnosed. After administration of 75 ml Iopromide (370 mg/ml) and a delay of 65 s, the whole abdomen and pelvis were scanned in a collimation of 4 x 2.5 mm and 12.5 mm table feed per rotation. The suspected tissue was marked by the freehand ROI option in every slice and the minimum, average and maximum densities were calculated. A local recurrence was suspected if maximum density was higher than 90 HU after admission of contrast media. In addition we calculated the maximum difference of density as the difference between maximum and minimum density.

The minimum and average densities showed no reliable differences for patients with or without local recurrence (minimum density 4 HU ( +/- 12 HU) vs. 13 HU ( +/- 21 HU), P = 0.23, average density 48 HU ( +/- 10 HU), vs. 48 HU ( +/- 17 HU)), P = 0.52. The patients suffering from local recurrence showed higher maximum densities and a higher maximum difference than the patients without recurrence (maximum density 111 HU ( +/- 13 HU) vs. 81 HU ( +/- 24 HU), P = 0.02, maximum difference 103 HU ( +/- 20 HU) vs. 76 HU ( +/- 31 HU), P = 0.06. These differences were not significant. We calculated a sensitivity of 0.6, a specificity of 0.83, a positive predictive value of 0.52 and an accuracy of 0.77.

It is not possible to diagnose a recurrent rectal cancer by density values alone.