Early prediction of histopathological response of rectal tumors after one week of preoperative radiochemotherapy using 18 F-FDG PET-CT imaging. A prospective clinical study
- Equal contributors
1 Department of Radiology, Rabin Medical Center, Beilinson Hospital, Petah Tiqva, Israel
2 Institute of Oncology, Davidoff Center, Rabin Medical Center, Beilinson Hospital, Petah Tiqva, Israel
3 Department of Nuclear Medicine, Rabin Medical Center, Beilinson Hospital, Petah Tiqva, Israel
4 Department of Pathology, Rabin Medical Center, Beilinson Hospital, Petah Tiqva, Israel
5 Department of Surgery B, Rabin Medical Center, Beilinson Hospital, Petah Tiqva, Israel
6 Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
7 Institute of Oncology, Kaplan Medical Center, Rehovot, Israel
8 Department of Nuclear Medicine, Assuta Medical Center, Tel Aviv, Israel
Radiation Oncology 2012, 7:124 doi:10.1186/1748-717X-7-124Published: 1 August 2012
Preoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC). Initial data suggest that the tumor’s metabolic response, i.e. reduction of its 18 F-FDG uptake compared with the baseline, observed after two weeks of RCT, may correlate with histopathological response. This prospective study evaluated the ability of a very early metabolic response, seen after only one week of RCT, to predict the histopathological response to treatment.
Twenty patients with LARC who received standard RCT regimen followed by radical surgery participated in this study. Maximum standardized uptake value (SUV-MAX), measured by PET-CT imaging at baseline and on day 8 of RCT, and the changes in FDG uptake (ΔSUV-MAX), were compared with the histopathological response at surgery. Response was classified by tumor regression grade (TRG) and by achievement of pathological complete response (pCR).
Absolute SUV-MAX values at both time points did not correlate with histopathological response. However, patients with pCR had a larger drop in SUV-MAX after one week of RCT (median: -35.31% vs −18.42%, p = 0.046). In contrast, TRG did not correlate with ΔSUV-MAX. The changes in FGD-uptake predicted accurately the achievement of pCR: only patients with a decrease of more than 32% in SUV-MAX had pCR while none of those whose tumors did not show any decrease in SUV-MAX had pCR.
A decrease in ΔSUV-MAX after only one week of RCT for LARC may be able to predict the achievement of pCR in the post-RCT surgical specimen. Validation in a larger independent cohort is planned.