Value of FDG-PET/CT Volumetry After Chemoradiotherapy in Rectal Cancer.

Background: Neoadjuvant chemoradiotherapy followed by an optimal surgery is the standard treatment for patients with locally advanced rectal cancer. FDG-PET/CT is commonly used as the modality for assessing the effect of chemoradiotherapy.

Objective: The purpose of this study was to investigate whether PET/CT-based volumetry could contribute to the prediction of pathological complete response or prognosis after neoadjuvant chemoradiotherapy.

Design: This was a retrospective cohort study.

Settings: This study was conducted at a single research center.

Patients: Ninety-one consecutive patients with locally advanced rectal cancer were enrolled between January 2005 and December 2015.

Intervention: Patients underwent PET/CT before and after neoadjuvant chemoradiotherapy.

Main Outcome Measures: Maximum standardized uptake value and total lesion glycolysis on PET/CT before and after neoadjuvant chemoradiotherapy were calculated using isocontour methods. Correlations between these variables and clinicopathological factors and prognosis were assessed.

Results: PET/CT-associated variables before chemoradiotherapy were not correlated with either clinicopathological factors or prognosis. Maximum standardized uptake value was associated with pathological complete response, but total lesion glycolysis was not. Maximum standardized uptake value correlated with ypT, whereas total lesion glycolysis correlated with both ypT and ypN. High total lesion glycolysis was associated with a considerably poorer prognosis; the 5-year recurrence rate was 65% and the 5-year mortality rate 42%, whereas in lesions with low total lesion glycolysis, these were 6% and 2%. On multivariate analysis, high total lesion glycolysis was an independent risk factor for recurrence (HR = 4.718; p = 0.04).

Limitations: The gain in fluoro-2-deoxy-D-glucose uptake may differ between scanners, thus the general applicability of this threshold should be validated.

Conclusions: In patients with locally advanced rectal cancer, high total lesion glycolysis after neoadjuvant chemoradiotherapy is strongly associated with a worse prognosis. Total lesion glycolysis after chemoradiotherapy may be a promising preoperative predictor of recurrence and death. See Video Abstract at http://links.lww.com/DCR/A464.