Radiation dose estimates of 186Re-hydroxyethylidene diphosphonate for palliation of metastatic osseous lesions : An animal model study

A common complication in patients with breast or prostate cancer is bone metastases causing pain. New radionuclide therapy methods have recently been proposed for palliation, including 186 Re-hydroxyethyl-idene diphosphonate ( 186 Re-HEDP). This paper reports on the local development of 186 Re-HEDP and the biodistribution studied in animals for eventual use in patients. Adult dose was computed assuming a 70 kg standard man. The 186 Re was labelled to HEDP using standard techniques. The biodistribution in five Chacma baboons (Papio ursinus) was studied. Doses ranging from 39.4 to 44.9 MBq kg -1 (mean 43.6 ± 2.8 MBq kg -1 ) were administered, corresponding to an adult human dose of 2960 MBq (80 mCi). Whole-body images of the animals were obtained with a dual-headed scintillation camera on an hourly basis for 6 h post-injection and then daily for 3 days. The bone, soft tissue, kidneys and urinary bladder were considered source organs and data from these organs were used in a compartmental model to obtain the mean residence times of the radionuclide in the different source organs. Radiation dose estimates for 186 Re-HEDP were subsequently obtained with the MIRDOSE 3 program. The estimated absorbed radiation doses to some of the organs (expressed in mGy MBq -1 ) were as follows: bone surface 1.69; kidneys 0.09; liver 0.04; ovaries 0.04; red marrow 0.75; total body 0.12; urinary bladder wall 0.43. 186 Re-HEDP yielded an effective dose of 0.17 mSv MBq -1 . The radiation dose delivered to the bone marrow in this study did not cause any detrimental effect to the baboons, indicating that locally produced 186 Re-HEDP is suitable for clinical use.