Three-dimensional radiotherapy target volume definitions for osteoarthritis - Consensus statement of the International Benign Target Volume Group (IBTVG).

Abstract

Low-dose radiotherapy (LDRT) is a minimally invasive treatment option for pain management in selected patients with osteoarthritis (OA). However, standardized and internationally accepted target volume definitions are still lacking. An international expert consortium of 15 institutions from Europe and the United States conducted a Delphi consensus process to define joint-specific target volumes based on the three-dimensional concept of the Clinical Target Volume (CTV). A standardized CT dataset ("homunculus") was used by all participants to ensure uniform anatomical reference for target volume delineation. Target volume definition includes inflammatory and OA-specific pathological features such as joint effusion, cysts, and subchondral sclerosis. The CTV encompasses the joint capsule and varies in its cranio-caudal extent among individual patients. Using joint-specific isocenter definitions - such as the midpoint between the femoral condyles for the knee joint - the three-dimensional boundaries of the CTV can be determined. This approach enables anatomically precise delineation of the target volume, ensuring inclusion of inflammation-relevant structures while excluding uninvolved bone and soft tissue. This international consensus statement provides practical guidance for a standardized three-dimensional target volume definition in the radiotherapy of OA. Accurate knowledge of joint anatomy and pathology, combined with precise target volume delineation and careful consideration of the clinical context, such as symptom distribution and the pattern of joint involvement, may support more consistent LDRT treatment planning for OA. These target volume definitions also provide a structured basis for future clinical studies and further clinical validation.