1. Department of Neurosurgery, Ibaraki Seinan Medical Center Hospital
2. Department of Neurosurgery, Tsukuba Medical Center Hospital
3. Department of Neurosurgery, Kobari General Hospital
4. Department of Neurosurgery, General Moriya Daiichi Hospital
5. Department of Neurosurgery of Ibaraki Prefectural Central Hospital
6. Department of Neurosurgery, Dokkyo Medical University Koshigaya Hospital
7. Department of Neurosurgery, Institute of Clinical Medicine, University of Tsukuba