Differentiating intrapulmonary metastases from different primary tumors via quantitative dual-energy CT based iodine concentration and conventional CT attenuation.

INTRODUCTION: To investigate the utility of quantitative dual-energy spectral CT derived iodine concentration (IC), in comparison with conventional CT attenuation, for the differentiation of pulmonary metastases from different primary malignancies.
MATERIALS AND METHODS: CT scans were performed on a dual-layer spectral CT. We retrospectively evaluated pulmonary metastases of 130 patients (77 men and 53 women, mean age 63, range 22-87) with primary bone (OS) (osteosarcoma; n = 6), breast (invasive-ductal adenocarcinoma; n = 17), colorectal (CRC) (adenocarcinoma; n = 27), head and neck (HNC) (squamous cell carcinoma; n = 17), kidney (RCC) (clear-cell renal cell carcinoma; n = 10), lung (adenocarcinoma; n = 12), pancreato-biliary (PBC) (adenocarcinoma; n = 18), prostate (adenocarcinoma; n = 5), soft tissue (undifferentiated pleomorphic sarcoma; n = 6), skin (malignant melanoma; n = 6), and urinary tract (transitional-cell carcinoma; n = 6) malignancies. Quantitative IC and conventional CT numbers (HU) were extracted and normalized to the thoracic aorta. Differences between the groups were assessed by pairwise t-tests with Holm-Sidak post-hoc p-value adjustment for multiple comparisons. Diagnostic accuracy was evaluated by receiver operating characteristic (ROC) analysis.
RESULTS: Significant differences in IC and HU were noted for pulmonary metastases from RCC (IC: 2.83 mg/ml; HU: 93.12) versus breast cancer (IC: 1.47 mg/ml, adjusted p < 0.05; HU: 59.57, adjusted p < 0.05), CRC (IC: 1.23 mg/ml, adjusted p < 0.001; HU: 49.82, adjusted p < 0.001) and HNC (IC: 1.54 mg/ml, adjusted p < 0.05; HU: 58.91, adjusted p < 0.01). Based on IC alone, significant differences were further observed between metastatic lesions from CRC versus OS (IC: 2.36 mg/ml, adjusted p < 0.001), PBC (IC: 2.16 mg/ml, adjusted p < 0.001) and urinary tract carcinoma (IC: 2.21 mg/ml, adjusted p < 0.05). Based on IC and HU, pulmonary metastases from OS, HNC and RCC may be differentiated from other pulmonary metastases (area under ROC curve, 0.69-0.79). The diagnostic accuracy to discriminate between pulmonary metastases from PBC and those from other malignancies was significantly higher based on IC as compared to HU (area under ROC curve, 0.66; p < 0.05); no significant differences in diagnostic accuracy were noted for other differentiations.
CONCLUSIONS: Our findings demonstrate the utility of both dual-energy CT derived quantitative IC and conventional CT attenuation values for the differential diagnosis in suspected pulmonary metastases of unknown origin, however giving preference to the use of IC.