Samarium-153-EDTMP in bone metastases

Thirty-five patients with painful bone metastases arising from a variety of tumor types underwent a clinical trial in which 153Sm-EDTMP was injected as a single intravenous dose. The injection ranged in amount from 330 MBq to 1110 MBq of 153Sm-EDTMP. Pain relief usually occurred within one week after administration. The duration of pain relief lasted from 2 to 17 weeks. A detectable degree of pain palliation was experienced by 80% of the treated patients; 54% reported substantial or complete pain relief. Due to the small number of patients, no clear-cut dose-related response was detectable. Moderate myelosuppression was observed in one patient (WHO grade III). The metastatic lesion-to-normal bone ratios remained constant (varying from 1.5 to 4.8) for at least 5 days post-injection. 153Sm cleared very rapidly from the blood. Less than 1% of the injected dose remained in circulation at 4 hours post-injection. No local accumulation of the tracer could be detected outside the skeleton. Urinary excretion was quite complete at 6 hours post-injection. The biodistributions of 153Sm-EDTMP and 99mTc-DPD are very similar in metastatic and normal bone; thus, bone scanning can be used for patient selection and followup. According to our results, it seems that higher doses of 153Sm-EDTMP can be given safely and without any irreversible myelosuppression.