Thirty-five patients with disseminated skeletal
metastases from a variety of
tumor types underwent clinical trial of
samarium-153 ethylenediaminetetramethylene
phosphonate (153Sm-EDTMP) on a day-patient basis. Individual beta radiation dosimetry was based on pharmacokinetic studies of a 20 mCi tracer dose of
153Sm-EDTMP. The retained skeletal activity varied unpredictably from 40% to 95% of the administered dose, but in all patients greater than 98% of the nonosseous activity was cleared in the urine within 6 hours. Prospective calculation of radiation dosimetry in each patient permitted an accurate dosage schedule based upon total red marrow exposure, starting at 100 cGy and escalating to 280 cGy to define the dose-limiting myelotoxicity.
Pain was relieved in 22 of 34 evaluable patients (65%) for periods ranging from 4 to 35 weeks, following a single administration of
153Sm-EDTMP. Recurrence of
pain responded to
retreatment with
153Sm-EDTMP in five of nine patients. The dose-limiting toxicity was myelosuppression manifested particularly by delayed
thrombocytopenia. Platelet counts less than 100 x 10(9)/L occurred in 42% of courses when bone marrow radiation absorbed dose exceeded 200 cGy. Myelosuppression was transient and platelet counts had recovered to pretreatment levels within 10 weeks of treatment.
153Sm-EDTMP is effective for the amelioration of
pain due to disseminated skeletal
metastases particularly with
carcinoma of breast or prostate where 83% of patients experienced
pain relief. In 15 of the 34 evaluable patients there was evidence of stabilization or regression of skeletal
metastases on radiographs and follow-up technetium-99m
methylene diphosphonate (99mTc-MDP) bone scans.