The aim of this study was to introduce a new quantification method for 153Sm-ethylenediaminetetramethylenephosphonate (EDTMP) and 186Re-(tin)1,1-hydroxyethylidene diphosphonate (HEDP) to separately measure bone uptake and soft-tissue retention of these radiopharmaceuticals. METHODS: Studies were performed on 23 men and 6 women undergoing radionuclide therapy for palliation of bone pain. Whole-body images were acquired at 3 min, 3-4 h, and 24-72 h after injection of 1,295 MBq 186Re-HEDP and 37 MBq 153Sm-EDTMP per kilogram of body weight. The activities for whole body, urinary bladder, and both thighs, as representative of soft tissue, were measured by region-of-interest technique. A background region of interest adjacent to the head was used to correct for bremsstrahlung. Bone uptake was calculated as initial whole-body activity minus urinary excretion and remaining soft-tissue activity. RESULTS: For 186Re-HEDP (n = 11) the mean bone uptake at 3 h after injection was 13.7% +/- 8.6% of initial whole-body activity. The remaining soft-tissue activity was 49.4% +/- 16.9%, and urinary excretion was 36.9% +/- 14.4%. At 24 h after injection, bone uptake reached a value of 21.8% +/- 9.0%. Urinary excretion increased to 65.3% +/- 12.8% according to a decreasing soft-tissue remainder activity of 12.8% +/- 5.4%. The corresponding results for 153Sm-EDTMP (n = 18) at 3 h after injection were 29.2% +/- 15.5% for bone uptake, 32.3% +/- 12.9% for urinary excretion, and 38.4% +/- 14.5% for soft tissue. At 24 h after injection, we calculated values of 47.7% +/- 11.2% for bone uptake, 39.5% +/- 13.8% for urinary excretion, and 12.7% +/- 4.7% for soft tissue. CONCLUSION: Bone uptake and soft-tissue retention for both 186Re-HEDP and 153Sm-EDTMP as obtained in this study agree well with the conventional 24-h whole-body retention measurements for these tracers. However, by this new scintigraphic quantification method, bone uptake and soft-tissue retention can be calculated separately, thus providing more detailed kinetic data and potentially improving the dosimetry of these radiopharmaceuticals in, for example, assessment of radiation dosage to bone and bone marrow.
