Perfusion CT measurements predict tumor response in rectal carcinoma.

PURPOSE

To evaluate the capacity of perfusion CT imaging to distinguish between complete and incomplete responders after neoadjuvant chemoradiation therapy for rectal carcinoma, with particular attention to segmentation technique.

MATERIALS AND METHODS

17 patients were evaluated in this prospective IRB-approved study. For each patient, a perfusion CT acquisition was obtained prior to the initiation of chemoradiation, at 1-2 weeks after the start of chemoradiation, and at 12 weeks after the start of chemoradiation therapy. From each dataset, three perfusion parameters were measured, each in two different ways: a region of interest incorporating only "hot spots" of greatest enhancement and whole-tumor measurements.

RESULTS

In univariate analysis, blood volume and permeability differed significantly between responders and non-responders. In logistic regression analysis evaluating predictors of the "complete response" outcome, only two predictors were retained as statistically significant: peak hot spot blood volume 1-2 weeks into therapy (OR 10.25, p = 0.0026) and hot spot permeability decline at 12 weeks after the initiation of therapy (OR 5.62, p = 0.03). The overall likelihood ratio test for this model supported the conclusion that hot spot blood volume and hot spot permeability decline were significant predictors of the complete pathologic response outcome (p < 0.0001).

CONCLUSION

In this pilot study, peak tumor blood volume and decline in tumor permeability, when measured in "hot spots" of greatest enhancement, were strong predictors of complete therapeutic response in rectal cancer after neoadjuvant therapy.