Kaique Moraes do Amaral, Rayama Moreira Siqueira, Nájua Abou Arab, Elba Etchebehere, Mariana da Cunha Lopes de Lima, Allan de Oliveira Santos, Celso Dario Ramos, Thiago Ferreira de Souza, Sérgio Quirino Brunetto, Edna Marina de Souza, Cleide Aparecida Moreira Silva, Carlos Augusto Real Martinez, Bárbara Juarez Amorim
The present study suggests that FDG-PET/CT provides valuable complementary information for response assessment after nCRT in rectal cancer and may assist multidisciplinary decision-making regarding organ-preserving strategies. Absence of residual uptake on post-treatment imaging and post-treatment SUVmax demonstrated high diagnostic accuracy for identifying complete responders.
OBJECTIVE: To evaluate qualitative and quantitative metabolic parameters on 18 F-fluorodeoxyglucose positron emission tomography/computed tomography [FDG PET/CT] for differentiating complete from incomplete response in patients with locally advanced rectal cancer after neoadjuvant chemoradiotherapy.
MATERIALS AND METHODS: This retrospective single-center study included 74 patients with locally advanced rectal cancer who underwent FDG PET/CT before and after neoadjuvant chemoradiotherapy. Patients were classified as good responders [complete clinical response, n = 34] or poor responders [n = 40]. Visual response was assessed using a five-point visual response score. Quantitative parameters included SUVmax, SUVmean, metabolic tumor volume, and total lesion glycolysis, using a fixed 41% threshold and best visual fit segmentation. Group comparisons, receiver operating characteristic analysis, and logistic regression were performed.
RESULTS: VRS grade 4 [no uptake post-treatment] demonstrated high specificity [95%] and positive predictive value [90.9%] for identifying good responders, with a sensitivity of 58.8%. Two false positives were observed [carcinoma in situ and mucinous tumor]. Significant quantitative differentiators included post-treatment SUVmax41% [p < 0.0001], SUVmaxBVF [p < 0.0001], SUVmean41% [p < 0.0001], SUVmeanBVF [p < 0.0001], post-treatment TLGBVF [p = 0.0164], ΔSUVmax [p = 0.0306], and ΔSUVmean41% [p = 0.0072]. Post-treatment SUVmax showed the highest accuracy, with an area under the curve [AUC] of 0.917.
CONCLUSIONS: The present study suggests that FDG-PET/CT provides valuable complementary information for response assessment after nCRT in rectal cancer and may assist multidisciplinary decision-making regarding organ-preserving strategies. Absence of residual uptake on post-treatment imaging and post-treatment SUVmax demonstrated high diagnostic accuracy for identifying complete responders.