Objective:To investigate the value of the nomogram based on quantitative parameters of dual-layer detector spectral CT and conventional CT features in preoperatively predicting tumor deposits (TDs) in colorectal cancer.Methods:This study was a case-control study. A total of 126 patients with pathologically confirmed colorectal cancer who underwent preoperative spectral CT scan from January 2022 to March 2023 in the First Affiliated Hospital of Soochow University were enrolled retrospectively. Patients were divided into TDs-positive group ( n=38) and TDs-negative group ( n=88) based on pathological results. The following conventional CT features were assessed: cT stage, cN status, uniformity of enhancement in the venous phase, pericolorectal fat invasion (PFI), maximum tumor diameter, and tumor location. The following quantitative parameters were also measured and calculated: the normalized iodine concentration (NIC) of lesions, the normalized effective atomic number (NZ eff), and the slope of the 40-100 keV spectral curve (K) in the arterial and venous phases, and the difference in NIC between the arterial and venous phases. Multivariate logistic regression analysis was used to select independent predictors of TDs and the nomogram based on spectral CT quantitative parameters and conventional CT features was constructed. The receiver operating characteristic curve was performed to evaluate the diagnostic performance of each parameter and model. DeLong test was used to compare the differences of area under the curve (AUC). Results:Statistically significant differences were found between the TDs-positive and TDs-negative groups for the cT stage, cN status, uniformity of enhancement in the venous phase, PFI, NIC, NZ eff, K in the venous phase and the difference in NIC between the arterial and venous phases ( P<0.05). After multivariate logistic regression analysis, the conventional CT feature model incorporated two features: uniformity of enhancement in the venous phase (OR=9.602, 95% CI 3.728-24.734, P=0.001) and PFI ( OR=2.881, 95% CI 1.177-7.049, P=0.020). The combined model of conventional CT features and spectral CT quantitative parameters incorporated three features: the difference in NIC between the arterial and venous phases ( OR=37.599, 95% CI 8.320-169.912, P=0.001), uniformity of enhancement in the venous phase ( OR=14.978, 95% CI 3.848-58.295, P=0.001), and PFI ( OR=4.013, 95% CI 1.320-12.760, P=0.015), and the nomogram was constructed. The AUC, sensitivity, and specificity of the nomogram for predicting TDs were 0.919 (95% CI 0.865-0.973), 84.2%, and 86.5%, respectively. The AUC of the conventional CT feature model was 0.796 (95% CI 0.707-0.885), which was lower than that of the nomogram, and the difference was statistically significant ( Z=3.87, P=0.001). Conclusion:Dual-layer spectral detector CT can be used to predict TDs in colorectal cancer preoperatively, and the nomogram based on quantitative parameters of dual-layer detector spectral CT and conventional CT features shows good diagnostic performance.