The physical characteristics of Sn-117m combined with the biodistribution of the compound tin-117m (Stannic, 4+) diethylenetriaminepentaacetic
acid (Sn-117m DTPA) suggest that it should be an excellent agent for the palliation of
pain from bony
metastases. Prior work has established the dosimetry and the safety for the material in human beings. The presence of low-energy conversion electrons should result in the relative sparing of the bone marrow while delivering a high radiation dose to sites of bony metastatic disease. Forty-seven patients with painful bone
metastases from various
malignancies were treated with Sn-117m
DTPA. The patients were assigned to five different dose levels ranging from 2.64 to 10.58 MBq (71-286 microCi) per kg of
body weight. Follow-up included review of
pain diaries, performance scores,
analgesic requirements, blood chemistries, and hematological assessment. Three patients received a second treatment. There was an overall response rate for relief of
pain of 75% (range, 60-83%) in the 40 treatments that could be evaluated. No correlation was apparent in this limited series between response rate and the five dose levels used. The relief was complete in 12 patients (30%). The time to onset of
pain relief was 19 +/- 15 days with doses < or = 5.29 MBq/kg and 5 +/- 3 days with doses > or = 6.61 MBq/kg. Myelotoxicity was minimal, with only one patient having a marginal grade 3 WBC toxicity. On the basis of our data, Sn-117m
DTPA should be an effective and safe
radiopharmaceutical for palliation of painful bony
metastases. A large-scale trial is warranted to evaluate it in comparison to other similar agents.