T-Staging and Target Volume Definition by Imaging in GI Tumors

Contrast-enhanced CT, magnetic resonance imaging and endoscopic ultrasound represent the mainstay imaging modalities for T-staging of GI-tract malignancies and radiotherapy planning. PET and PET/CT have a complementary role. In esophageal carcinoma and cancer of the esophagogastric junction, PET imaging improves definition of the local tumor extent and detection of involved locoregional lymph nodes, leading to enhanced target volume definition. Consequently, addition of functional imaging leads to improved local disease control and reduced radiation-induced risks. In gastric cancer, the role of PET and PET/CT is less clear. Reduced sensitivity and specificity reduce their utility for tumor delineation. Due to an obvious lack of clinical trials, no definite conclusions can be drawn on the use of PET or PET/CT for radiation treatment planning in gastric cancer. In colorectal cancer, functional imaging has added value regarding the detection of distant metastases. PET/CT is therefore recommended for whole-body staging in patients with a high risk for presence of metastatic disease, significantly influencing the decision making process. In pancreatic cancer, sensitivity and specificity of PET imaging using FDG as the tracer can be reduced by coexisting inflammatory or diabetic conditions. Therefore, its use for T-staging as well as radiotherapy planning remains challenging. Molecular imaging using more specific radiotracers addressing hallmarks of cancer or tumor specific antigens may improve accuracy of functional imaging in pancreatic cancer and other GI-tract malignancies.