177Lu-EDTMP - A bone pain palliating agent: Biodistribution and skeletal uptake in osseous metastatic patients

Objectives EDTMP (Ethylene Diamine Tetramethylene Phosphate) labeled with Lutetium-177 has been proposed as a potential radiopharmaceutical for pain palliation resulting from the osseous metastases.The primary goals of the study were to evaluate biodistribution, to measure bone uptake (by scintigraphy and urinary excretion of 177Lu-EDTMP), and to assess preferential localization of 177Lu-EDTMP in bony lesions.

Methods 177Lu- EDTMP was administered in escalating amounts from 699 to 2600 MBq to 16 patients with skeletal metastases; 13 males with prostate cancer and 3 females with breast cancer. 177Lu-EDTMP images were acquired on dual head gamma camera, at 30 min,then 4 and 24 hrsto determine the bone uptake. Cumulative urine activity was also measured at 4 and 24 hrs. The whole-body activities were measured by region-of-interest technique.

Results Compete concordance was found between the 99mTc-MDP and 177Lu-EDTMP images. The mean bone uptake was 69.8±21.26% of initial whole-body activity at 4 hrs after injection, reaching a value of 71.11±17.04% at 24 hrs. Values for bone activity determined by imaging and by urine counting, respectively, were concordant in all patients. Cumulative urinary excretion was 21.58±14.67% at 4 hrs and 30.90±17.64% at 24 hrs. A positive linear correlation was observed between bone uptake and extent of bone metastases.

Conclusions 177Lu-EDTMP has adequate bone uptake, rapid urinary excretion, and prolonged retention of activity in bones. Bone uptake calculated from scintigraphic imaging may provide a more accurate assessment of radiation dosimetry to bone and to bone marrow deriving from 177Lu-EDTMP administered for therapeutic purposes. Our preliminary results also indicate that 177Lu-EDTMP is a promising radiotherapeutic agent for palliative treatment of metastatic bone cancer pain.

Research Support International Atomic Energy Agency (IAEA