The use of 186Re(Sn)-HEDP for pain relief in the palliative treatment of bone cancers

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 186Re(Sn)-HEDP. This paper reports on the local development of 186Re(Sn)-HEDP and the biodistribution studied in animals for eventual use in patients. The 186Re was labelled to HEDP using standard techniques. Initially the biodistribution in five Chacma baboons was studied. Doses ranging from 39.4 MBq/kg to 44.9 MBq/kg (mean 43.6+-2.8 MBq/kg) were administered which corresponded with an adult human dose of 2960 MBq (80 mCi). Whole body images of the animals were obtained with a dual detector scintillation camera on an hourly basis for six hours 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 186Re(Sn)-HEDP were subsequently obtained with the MIRDOSE 3 program. Subsequent to the animal study, the palliative effect of the 186Re(Sn)-HEDP was evaluated in ten patients with primary prostate cancer using the pain scale suggested by the World Health Organization. Estimated absorbed radiation doses (expressed in mGy/MBq) to some of the organs of baboons were: 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. 186Re(Sn)-HEDP yielded an effective dose of 0.17 mSv/MBq in the animal study and 0.16 mSv/MBq in humans. Positive palliation was obtained in seven patients, but pain levels increased after 8 weeks. The radiation dose delivered to the bone marrow in this study did not cause any detrimental effect to the baboons or the humans, indicating that the locally produced 186Re(Sn)-HEDP is suitable for clinical use. (author)