¹⁸Fluoro-deoxy-glucose positron emission tomography in assessing tumor response to preoperative chemoradiation therapy for locally advanced rectal cancer

Background This study aims to evaluate the efficacy of ¹⁸F-FDG PET in assessing tumor response after preoperative chemoradiation therapy (CRT) for rectal cancer. Methods Maximum standardized uptake value (SUV) was measured for 37 patients who underwent ¹⁸F-FDG PET before and 4 weeks after completion of preoperative CRT. Pre-SUV, post-SUV, the difference between pre- and post-SUV (ΔSUV), and reduction rate (RR) were correlated with tumor response. Results A lower mean post-SUV and a higher mean RR were shown in good tumor response (T-downstaging(+) and tumor regression grade 1, 2). Considering pathologic complete response (pCR), the mean post-SUV and the mean RR were significantly different between pCR (+) patients (N = 13) and pCR (-) patients (N = 24) (2.7 vs. 4.8, P < 0.001, 73.9% vs. 58.7%, P = 0.009). With a 3.35 cut-off value for the post-SUV by receiver operating characteristic analysis, 84.6% sensitivity, 79.2% specificity, and 81.2% overall accuracy were obtained for discriminating between pCR (+) and pCR (-) (area under the curve = 0.885, P < 0.001). Conclusions ¹⁸F-FDG PET is potentially useful as a method for assessing tumor response after preoperative CRT for rectal cancer. Post-SUV and RR were significantly associated with pathological treatment response, especially in pCR.