To determine the utility of fluorodeoxyglucose-positron emission tomography-computed tomography scan in predicting pathological response in operated carcinoma rectum patients after initial neoadjuvant chemoradiation

Background: The objective of this study was to determine whether [F-18] -fluorodeoxyglucose-positron emission tomography-computed tomography (FDG-PET CT) scan could predict the pathological response in carcinoma rectum patients after surgery in patients receiving neoadjuvant concurrent chemoradiotherapy (NACCRT). Setting and Design: A prospective study was carried out from March 2015 to March 2017; 39 patients of histopathologically proven, locally advanced, potentially operable, of adenocarcinoma rectum were included in the study. Methods: Patients had a pretreatment FDG-PET-CT scan and repeat scan after 6-8 weeks of NACCRT. The change in mean maximum standardized uptake value ([%Delta SUVmax]) was compared with the tumor regression grade (TRG) in the postoperative histology. TRG of 1 and 2 was deemed responders and 3-5 was nonresponders. Statistical Analysis: Chi-square test, one-way ANOVA, and receiver operating characteristics curve analysis were used. All analyses were done using SPSS 17.0 version. Results: In 61.5% responders receiving NACCRT, the SUV fell from 10.91 +/- 3.70 to 4.14 +/- 1.73, respectively, while in 38.5% nonresponders, SUV fell from 11.65 +/- 2.66 to 4.23 +/- 1.3. SUV.% was 63.03 +/- 10.17 in nonresponders and 61.32 +/- 11.81 in responders with a nonsignificant P = 0.646. The P value did not reach a statistical significance as far as reduction in SUV values pre-and post-NACCRT is concerned in both responders as well as nonresponders. Conclusion: Hence, we concluded that assessment with FDG PET CT scan in carcinoma rectum patients' postneoadjuvant treatment cannot be the only imaging modality or assessing the response and postoperative histopathology remains the gold standard.