Caren van Roekel

50 Chapter 2 7.2. Functional imaging with 18 FDG-PET CT and somatostatin receptor analogue Functional imaging modalities may overcome the drawbacks of morphologic based treatment assessment. The backbone of oncologic imaging is 18 F-FDG- PET. Most malignancies have a high FDG uptake and this can be assessed both qualitatively and quantitatively during follow up. However, not all tumors show a high FDG uptake. Neuro-endocrine neoplasms G1/2 (Ki67<20%) are not well visualized by 18 F-FDG-PET imaging. These tumors express somatostatin receptors and this has led to the development of molecular imaging with radiolabelled somatostatin analogues. Gallium-68 is a positron-emitting isotope and a 68 Ga-somatostatin analogue ( 68 Ga-DOTATATE/- TOC/-NOC) PET scan is proven to be superior to 18 F-FDG-PET imaging in the detection and follow up of neuro-endocrine neoplasms (100, 101). 7.3. Response evaluation There is a variety of established response criteria. Most are based on the change in size of lesions, but since the rise of functional imaging also quantitative response criteria have been determined. The most widely used criteria, the RECIST, mRECIST and PERCIST, will be briefly discussed. 7.3.1. RECIST 1.1. The Response Evaluation Criteria In Solid Tumors (RECIST) have been developed in 2000 and were revised in 2009. The rationale behind these criteria is that objective response (shrinkage of the tumor) and time to progression are important endpoints in clinical trials. These endpoints are used to measure treatment effect, and tumor shrinkage is believed to positively influence overall survival. At baseline, two target lesions per organ, with a maximum of five lesions in total, have to be chosen. The longest diameter of the lesions must be measured and the lesions should be at least 10 mm in size if the CT scan has a slice thickness ≤5 mm. Usually, the biggest and most well-defined lesions are chosen as target lesions.