Interobserver agreement on definition of the target volume in stereotactic radiotherapy for pancreatic adenocarcinoma using different imaging modalities
Eleni Gkika, Dejan Kostyszyn, Tobias Fechter, Christos Moustakis, Floris Ernst, Judit Boda‐Heggemann, Gustavo R. Sarria, Karin Dieckmann, Sophie Dobiasch, Marciana Nona Duma, Fabian Eberle, K. Kroeger, B. Häussler, Víctor Izaguirre, Danny Jazmati, Stefan Lautenschläger, Fabian Lohaus, Frederick Mantel, J. Menzel, S. Pachmann, Matea Pavic, Kalinka Radlanski, Oliver Riesterer, S. Gerum, Falk Roeder, Jochen Willner, Steffen Barczyk, Detlef Imhoff, Oliver Blanck, Andrea Wittig, Matthias Gückenberger, Anca‐L. Grosu, Thomas Brunner
Abstract
PURPOSE: The aim of this study was to evaluate interobserver agreement (IOA) on target volume definition for pancreatic cancer (PACA) within the Radiosurgery and Stereotactic Radiotherapy Working Group of the German Society of Radiation Oncology (DEGRO) and to identify the influence of imaging modalities on the definition of the target volumes. METHODS: Two cases of locally advanced PACA and one local recurrence were selected from a large SBRT database. Delineation was based on either a planning 4D CT with or without (w/wo) IV contrast, w/wo PET/CT, and w/wo diagnostic MRI. Novel compared to other studies, a combination of four metrics was used to integrate several aspects of target volume segmentation: the Dice coefficient (DSC), the Hausdorff distance (HD), the probabilistic distance (PBD), and the volumetric similarity (VS). RESULTS: For all three GTVs, the median DSC was 0.75 (range 0.17-0.95), the median HD 15 (range 3.22-67.11) mm, the median PBD 0.33 (range 0.06-4.86), and the median VS was 0.88 (range 0.31-1). For ITVs and PTVs the results were similar. When comparing the imaging modalities for delineation, the best agreement for the GTV was achieved using PET/CT, and for the ITV and PTV using 4D PET/CT, in treatment position with abdominal compression. CONCLUSION: Overall, there was good GTV agreement (DSC). Combined metrics appeared to allow a more valid detection of interobserver variation. For SBRT, either 4D PET/CT or 3D PET/CT in treatment position with abdominal compression leads to better agreement and should be considered as a very useful imaging modality for the definition of treatment volumes in pancreatic SBRT. Contouring does not appear to be the weakest link in the treatment planning chain of SBRT for PACA.