A 64-year-old man with castration-resistant prostate cancer received 223Ra injection to treat bone metastases. The patient underwent a 223Ra SPECT scan after the first 223Ra injection in which there was increased uptake all over the spine. Spine-to-background activity ratio in the patient was approximately three times greater than normal spine-to-background activity ratios in 223Ra SPECT obtained from the other patients. Eight days after the fifth injection, the patient exhibited a very poor neurologic examination and died of intracranial hemorrhage due to severe thrombocytopenia (platelet counts, 23,000/mm3). The extensive radiation to the spine may have enhanced myelophthisic process in this case.