The Efficiency of 18F-FDG-PET/CT in Assessment of Tumor Response to Preoperative Chemoradiation Therapy for Locally Recurrent Rectal Cancer

Abstract Background:Locally recurrent rectal cancer (LRRC) remains a major problem after curative resection of primary rectal cancer. A noninvasive biomarker that accurately evaluates the disease status and assesses the treatment response with prognostic value is critically needed to optimize the treatment plan. This study assesses the effectiveness of PET/CT evaluation of preoperative chemoradiation therapy (CRT) in patients with LRRC.Patients and Methods:Since 2004, we have been performing preoperative CRT to improve local tumor control and survival. Between 2004 and 2013, 40 patients with LRRC underwent preoperative CRT (radiation; 50 Gy/25 fractions, chemotherapy; irinotecan plus UFT/leucovorin ) and radical surgery, and underwent 18F-FDG-PET/CT before and 3 weeks after the completion of CRT. The maximum standardized uptake value (SUVmax) of the pre-CRT scan (Pre-SUV) and the post-CRT scan (Post-SUV) were measured. The predictive ability of 18F-FDG-PET and CT/MRI response assessment were evaluated.Results:The mean Pre-SUV was significantly higher than Post-SUV (8.2±6.1, vs 3.8±4.0; P < 0.0001). Following CRT, 17/40 patients (42.5%) were classified as responders according to Mandard tumor regression grade (TRG1-2). The mean Post-SUV was significantly lower in responders than in nonresponders (2.0±1.7 vs 5.1±3.9; P = 0.0038). Pathological response was not correlated with the response as evaluated by CT (P > 0.9999) or MRI (P > 0.9999). Multivariate regression analysis identified Post-SUV as an independent predictor of local re-recurrence-free survival (P = 0.0383) and for overall survival (P = 0.0195). Conclusions:PET/CT is useful in assessing tumor response to preoperative CRT for LRRC and predicting prognosis after surgery.