Rhenium-186(Sn)-1,1-hydroxyethylidene diphosphonate (186Re-HEDP) has been used for palliation of metastatic bone pain. The purpose of this study was to find a relationship between the bone marrow absorbed dose and the toxicity, expressed as the percentage decrease in the peripheral blood platelet count.
Methods: The bone marrow absorbed dose was calculated according to the MIRD model using data obtained from ten treatments of patients suffering from metastatic prostate cancer; noninvasive and pharmacokinetic methods were used. The bone marrow doses were related to toxicity using the pharmacodynamic sigmoid Emax model.
Results: The mean bone marrow absorbed doses using the noninvasive and pharmacokinetic methods were in a close range to each other (1.07 mGy/MBq and 1.02 mGy/MBq, respectively). There was a good relationship between the toxicity and the bone marrow absorbed dose (r = 0.80). Furthermore, the EDrm50 (i.e., the bone marrow absorbed dose producing a 50% platelet decrease) to bone marrow for 186Re-HEDP was on the order of 2 Gy.
Conclusion: Although the function of normal bone marrow is affected by metastases in patients with metastatic bone disease, the MIRD model can be used to relate toxicity to the bone marrow absorbed dose after a therapeutic dosage of 186Re-HEDP.