Samarium-153-EDTMP Biodistribution and Dosimetry Estimation

Fifty-two patients were treated with single doses of 153Sm-EDTMP in a Phase I escalating dose protocol for palliation of bone pain from metastatic prostate carcinoma. Samarium-153 (T1/2 46.3 hr), maximum beta-particle energies 810 keV (20%), 710 keV (30%), 640 keV (50%), gamma photon 103 keV (28%), was complexed to the tetraphosphonate chelate, EDTMP. Five groups of patients were treated at doses of 1.0, 1.5, 2.0, 2.5, and 3.0 mCi/kg to evaluate toxicity from treatment. Patients were screened prior to treatment and followed after treatment with 99mTc-MDP bone scans. Biodistribution data on this group of patients were acquired and showed rapid uptake of 153Sm-EDTMP into bone with complete clearance of nonskeletal radiotoxicity by 6-8 hr. Also included are complete sets of dosimetry estimations on an additional seven patients who received 0.5 mCi/kg 153Sm-EDTMP Ca++ as part of a multiple dose therapy trial. Estimated radiation absorbed doses to bone surfaces averaged 25,000 mrad/mCi (6686 Gy/MBq), and urinary bladder doses averaged 3600 mrad/mCi (964 Gy/MBq).