Repeated radionuclide therapy of bone metastases with Rhenium-188 HEDP: A kinetic study

1793 Objectives: The aim of this study was to evaluate effective halflife and uptake of Re-188 HEDP in normal tissue and bone metastases. Methods: An activity of 3000+-370 MBq Re-188 HEDP was administered to 26 patients (37 therapies) with multifocal bone metastases of prostate carcinoma. Nineteen patients received a single injection, 7 patients underwent repeated injections. For kinetic calculations, five static whole-body scans were acquired after each application (directly p.i., 1.5, 18, 24, and 42 hours p.i., PRISM2000/Philips, MEGP). Using the ROI-technique, 1-3 metastases, left and right femur, soft tissue and whole body were evaluated. From the extracted values, we calculated the following parameters: mean effective halflives (eff HL), the eff HL-ratios of soft tissue/femur and metastases/femur (individually for all patients) and the uptake in the metastases expressed as the ratio of metastasis/whole body. Results: For the eff HL of soft tissue, femur and metastases we obtained 10.0 h +-2.5, 9.6 h +- 2.8 and 15.3 h +-9.1, respectively. The eff HL-ratios soft tissue/femur and metastases/femur were calculated with 1.18+-0.52 and 1.61+-1.5, respectively. The mean uptake of all metastases was 1.42% +-1.16. The uptake of the metastases that underwent repeated therapies, was 1.23% +-0.89, 1.10% +-0.63 and 1.34% +-0.74 for the first, second and third therapy, respectively. This means that the uptake during the second therapy was in the mean 11% lower than during the first (in 5 patients higher, 7 diminished and 2 unchanged). Compared with the second, the uptake during the third therapy was 21% higher ( in 3 patients increased, 4 diminished). The eff HL of repeatedly treated metastases was 15.29 h +-3.65, 20.92 h +-7.9 and 18.85 h +-7.3 during the first, second and third therapy, respectively. Thus the eff HL during the second therapy was 37% higher than in the first one (9 pat. increased, 3 diminished). Compared with the second, the third treatment showed a reduction of eff HL by 10% (3 pat. increased, 3 diminished). Conclusions: The biological elimination in the metastases was lower than that in soft tissue and femur indicating a higher residence time in the metastases. In repeatedly treated bone metastases, the uptake remained constant, the effective halflife (and therefore the irradiation time) was prolonged. These data confirm that higher radiation doses can be achieved by repeated radionuclide treatments.