[en] Changes of bone scintigraphy with Tc-99m-MDP (methylene diphosphonate) and CT scan after irradiation were discussed with 28 lesions in 22 cases of metastatic bone tumor. Methods: 1) Co-60 irradiation: 200 rad/day x 5 times in a week and 5,000 - 6,000 rad in total dose were prearranged for radiotherapy. 2) Bone scintigraphy was taken by PHO/GAMMA LFOV 3 hours after the injection of Tc-99m-MDP with 10 mCi. 3) CT scan was performed by EMI-scanner CT 5005/12 and Ca concentration was calculated from EMI units. Results: 1) In bone scintigraphy, many of lesions treated with prearranged dose in total showed decreased or unchanged accumulation after irradiation, but in Ca concentration by CT, the lesions treated with a break showed increased concentration and the lesions continuously treated or given up showed no tendency. 2) The osteolytic lesions in CT images had no tendency to change their findings of bone scintigraphy but their Ca concentration measured by CT image was decreased after irradiation. 3) Changes of bone scintigraphy and CT image were not shown a clear correlation but there was a tendency as follows: In cases of decreased abnormal accumulation in postirradiative bone scintigraphy, Ca concentration of the lesion was increase, and in cases with increased accumulation, Ca concentration was decreased. (author)