When treating patients with the Leksell Gamma Knife®, the patient is attached to the device via an adapter. The adapter is the interface between the Leksell Gamma Knife® and the immobilization system used for the treatment. The Leksell Gamma Knife® has three types of adapters for patient fixation, the g-frame adapter, the vantage adapter, and the mask adapter. Elekta has become aware that a Quality Assurance (QA) procedure was initiated while the adapter was not properly locked to the patient positioning system of the Leksell Gamma Knife® as a result, the QA check failed.