1. Anesthesiology and Pain Relief Centre, The University of Tokyo Hospital, Hongo, Tokyo 113‑0033, Japan
2. Department of Pain and Palliative Medicine, The University of Tokyo Hospital, Hongo, Tokyo 113‑0033, Japan
3. Department of Pain and Palliative Medical Sciences, Faculty of Medicine, The University of Tokyo, Hongo, Tokyo 113‑0033, Japan