Margriet Kwint

General introduction and outline of thesis 1 13 (oligo) metastases in for example brain, liver, lungs, bone and adrenal glands. Besides SABR, radiofrequency ablation and surgery are also frequently used techniques to treat (oligo) metastases. Between 2008 and 2016 we performed an observationally study in patients that were selected during a tumor board meeting to have a radical approach of oligometastatic NSCLC (32). In this time period a radical approach for oligo metastatic NSCLC was not standard of care (28, 33). Recent years, evidence is growing that a radical treatment for oligometastatic NSCLC is beneficially. Recently published phase 2 trials, showed a significantly improved OS in oligometastatic NSCLC patients who were treated with a radical treatment on all metastases (26, 30). At the moment, phase 3 studies are ongoing (34, 35) to establish the role of such a radical approach in NSCLC finally. This will hopefully gather evidence, to confirm the benefit seen in randomized phase II trials of this therapeutic approach for oligometastatic disease, and will teach us which patient to select. Image Guided radiotherapy The introduction of the 18 F-fluorodeoxyglucose positron emission tomography (FDG- PET) combined with CT, had a major impact on accurate staging of lung cancer patients. An FDG-PET is able to differentiate between an elevated glucose metabolism in tissues, which is characteristic for cancer and inflammation, and leads to a more accurate tumor staging; e.g. a better distinction between tumor and atelectasis or detection of distant metastasis (36). By combining the FDG-PET with the RT-planning CT, the delineation uncertainties of the gross tumor volume (GTV) are reduced (37). To take into account microscopic tumor extension, the GTV is expanded to the clinical target volume (CTV). To correct for geometric uncertainties, this CTV is expanded to a planning target volume (PTV) (38). In our institute the ‘van Herk’ margin recipe is used (39), which corrects for random and systemic errors and incorporates the size of the margin on individualized respiratory tumor motion. Image guide radiotherapy (IGRT) visualizes the tumor and organs at risk (OAR) in the treatment room and corrects for differences between treatment planning and delivery. In the past, electronic portal imaging devices (EPID) with the use of megavolt or kilovolt imaging were used making 2D images. Nowadays most modern radiotherapy departments use linear accelerator integrated Cone Beam CT’s (CBCT) for imaging during radiotherapy (40). A CBCT is a type of CT-scanner, which can make in-room 3D and 4D (kV) images of the patient before, during and after the treatment using a single