Objective To explore the value of spectral CT parameters of primary tumor lesions and largest peritumoral nodule in predicting tumor deposits (TDs) in colorectal cancer (CRC).

Methods Clinical, imaging, and pathological data of 121 patients with pathologically confirmed CRC (64 males and 57 females; aged (64.8±11.4) years) treated at Huizhou Central People′s Hospital from March 2022 to May 2024 were retrospectively analyzed. Patients were divided into the TDs-positive and TDs-negative groups based on pathological findings. The spectral CT parameters of primary tumor lesions and largest peritumoral nodule were measured, including the iodine concentration and spectral curve slope (k) during arterial and venous phases, as well as the short-axis diameter of the largest peritumoral nodule. Spectral CT parameters and short-axis diameter of nodule were compared between groups. Two independent sample t test (homogeneity of variance) was used to compare the measurement data in accordance with normal distribution between groups. The Mann-Whitney U test was used to compare measurement data that deviated from the normal distribution between groups. The χ² test was used to compare count data between groups. Binary Logistic regression was performed to establish spectral CT combined parameter models using arterial and venous phase parameters and short-axis diameter of nodule. Receiver operating characteristic (ROC) curves were used to evaluate diagnostic performance, and the area under curve (AUC) was calculated.

Results There were 33 patients in the TDs-positive group and 88 patients in the TDs-negative group. The TDs-positive group showed significantly lower iodine concentration and k values in the largest peritumoral nodule compared with the TDs-negative group (arterial phase iodine concentration: 15.49 (11.56, 18.56)×100 ng/cm³ vs. 18.35 (14.58, 24.08)×100 ng/cm³, arterial phases k: 1.84 (1.39, 2.21) vs. 2.17 (1.73, 2.85); venous phase iodine concentration: (20.26±4.35)×100 ng/cm³ vs. (24.06±5.14)×100 ng/cm³, venous phases k: 2.40±0.51 vs. 2.86±0.61; Z=−3.425, −3.416; t=3.767, 3.780; all P<0.001). Conversely, the TDs-positive group exhibited higher iodine concentration and k values in primary tumor lesions and largest peritumoral nodule short-axis diameters compared with the TDs-negative group (arterial phase iodine concentration: (17.28±3.18)×100 ng/cm³ vs. (15.76±3.61)×100 ng/cm³, arterial phase k: 2.05±0.38 vs. 1.87±0.43; venous phase iodine concentration: (22.64±3.23)×100 ng/cm³ vs. (21.00±2.97)×100 ng/cm³, venous phase k: 2.69±0.39 vs. 2.49±0.35; largest peritumoral nodule short-axis diameters: 7.10 (5.55, 9.40) mm vs. 6.00 (4.83, 6.88) mm; t=−2.134, −2.186, −2.642, −2.661; Z=−2.664; all P<0.05). Patients with lymph node metastasis, higher N stage, and elevated carcinoembryonic antigen levels had increased TDs risk (χ²=−3.250, −6.478, 5.671; all P<0.05). ROC curve analysis revealed that the venous phase spectral CT parameters combined model achieved excellent predictive performance for TDs (AUC=0.834, best cut-off=0.303, sensitivity=0.788, and specificity=0.761).

Conclusion The spectral CT parameters of the primary tumor lesions and largest peritumoral nodule in CRC have predictive value for TDs, with the spectral CT combined parameter models in the venous phase showing optimal predictive performance.