Superior Tumor Detection for 68Ga-FAPI-46 Versus 18F-FDG PET/CT and Conventional CT in Patients with Cholangiocarcinoma

Management of cholangiocarcinoma is among other factors critically determined by accurate staging. Here, we aimed to assess the accuracy of PET/CT with the novel cancer fibroblast-directed ⁶⁸Gafibroblast activation protein (FAP) inhibitor (FAPI)-46 tracer for cholangiocarcinoma staging and management guidance. Methods: Patients with cholangiocarcinoma from a prospective observational trial were analyzed. ⁶⁸Ga-FAPI-46 PET/CT detection efficacy was compared with ¹⁸F-FDG PET/CT and conventional CT. SUV_max/tumor-to-background ratio (Wilcoxon test) and separately uptake for tumor grade and location (Mann-Whitney U test) were compared. Immunohistochemical FAP and glucose transporter 1 (GLUT1) expression of stromal and cancer cells was analyzed. The impact on therapy management was investigated by pre- and post-PET/CT questionnaires sent to the treating physicians. Results: In total, 10 patients (6 with intrahepatic cholangiocarcinoma and 4 with extrahepatic cholangiocarcinoma; 6 with grade 2 tumor and 4 with grade 3 tumor) underwent ⁶⁸Ga-FAPI-46 PET/CT and conventional CT; 9 patients underwent additional ¹⁸F-FDG PET/CT. Immunohistochemical analysis was performed on the entire central tumor plain in 6 patients. Completed questionnaires were returned in 8 cases. Detection rates for ⁶⁸Ga- FAPI-46 PET/CT, ¹⁸F-FDG PET/CT, and CT were 5, 5, and 5, respectively, for primary tumor; 11, 10, and 3, respectively, for lymph nodes; and 6, 4, and 2, respectively, for distant metastases. ⁶⁸Ga-FAPI-46 versus ¹⁸F-FDG PET/CT SUV_max for primary tumor, lymph nodes, and distant metastases was 14.5 versus 5.2 (P = 0.043), 4.7 versus 6.7 (P = 0.05), and 9.5 versus 5.3 (P = 0.046), respectively, and tumor-to-background ratio (liver) was 12.1 versus 1.9 (P = 0.043) for primary tumor. Grade 3 tumors demonstrated a significantly higher ⁶⁸Ga-FAPI-46 uptake than grade 2 tumors (SUV_max, 12.6 vs. 6.4; P = 0.009). Immunohistochemical FAP expression was high on tumor stroma (~90% of cells positive), whereas GLUT1 expression was high on tumor cells (~80% of cells positive). Overall, average expression intensity was estimated as grade 3 for FAP and grade 2 for GLUT1. Positive ⁶⁸Ga-FAPI-46 PET findings led to a consequent biopsy workup and diagnosis of cholangiocarcinoma in 1 patient. However, patient treatment was not adjusted on the basis of ⁶⁸Ga-FAPI-46 PET. Conclusion: ⁶⁸Ga-FAPI-46 demonstrated superior radiotracer uptake, especially in grade 3 tumors, and lesion detection in patients with cholangiocarcinoma. In line with this result, immunohistochemistry demonstrated high FAP expression on tumor stroma. Accuracy is under investigation in an ongoing investigator-initiated trial.

Improving radiation physics, tumor visualisation, and treatment quantification in radiotherapy with spectral or dual-energy CT

Over the past decade, spectral or dual‐energy CT has gained relevancy, especially in oncological radiology. Nonetheless, its use in the radiotherapy (RT) clinic remains limited. This review article aims to give an overview of the current state of spectral CT and to explore opportunities for applications in RT.

In this article, three groups of benefits of spectral CT over conventional CT in RT are recognized. Firstly, spectral CT provides more information of physical properties of the body, which can improve dose calculation. Furthermore, it improves the visibility of tumors, for a wide variety of malignancies as well as organs‐at‐risk OARs, which could reduce treatment uncertainty. And finally, spectral CT provides quantitative physiological information, which can be used to personalize and quantify treatment.