 The IMMO-LDRT01 study aims for the first time to analyze in detail the immune status of patients suffering from inflammatory, chronic joint diseases before, during and after LD-RT in a longitudinal manner. The multi-color flow cytometry-based assay will allow determining over 30 immune cell subsets and additionally their activation status. Further, biodosimetry will be performed with the whole-blood samples to get hints about dose that the immune cells are exposed to. This will be performed with national and international co-operation partners. 