Collision avoidance is a key issue for patient safety in radiation therapy (RT). Noncoplanar treatment fields (P. Dong et al. 2013) and more complex immobilization devices (Dougherty et al. 2021) offer improved treatment quality, but come with increased risk of collisions between gantry, couch, and patient (Nguyen et al. 2019). Various strategies based on patient’s computed tomography (CT) imaging have been proposed to predict collisions (Miao et al. 2020), but due to limited CT length the patient’s full body position often remains unknown. (Wang et al. 2021).