Radionuclide Therapy for Oncology – Current Status and Future Aspects- RHENIUM-186-HEDP DOSIMETRY AND MULTIPLE BONE METASTASES PALLIATION THERAPY EFFECTS Lyra M 1 , Papanikolos G 1 , Phinou P 2 , Frantzis A P 1 , Jordanou J 1 , Limouris G S 1 1. Introduction Skeletal metastases are a most common form of metastatic cancer, appearing in the vast majority of patients with breast and prostate cancer and frequently in patients with lung cancer, renal cancer, thyroid cancer and multiple myeloma. These metastases are a major cause of serious morbidity resulting in severe bone pain, hypercalcemia, loss of function following pathological fractures and neurological symptoms from nerve compression [1]. Since survival of these patients is estimated up to 4 years, more in some cases, improving quality of life by pain palliation is the main goal. Although bone pain, confined to single sites, usually responds favorably to local external beam radiotherapy, in cases of widespread bone metastases where half – or whole – body irradiation is appropriate, considerable side effects such as bone marrow suppression, gastrointestinal symptoms and radiation pneumonitis are caused by the fact that all irradiated tissues receive similar doses. Therefore delivering high doses to tumor cells while limiting radiation dose to normal tissue, is the key for successful palliation [1,2,3]. Such a combination can be achieved with the application of beta – emitting radionuclides conjugated to bone – seeking pharmaceuticals, such as pyrophosphate analogues. Rhenium – 186(Sn) – 1,1 hydroxyethylidene diphosphonate ( 186 Re – HEDP) is a radiopharmaceutical that combines selective localization in osteoblastic skeletal metastases with favorable radiation characteristics concerning pain palliation as well as dosimetric estimations and scintigraphic imaging . Unavoidable red marrow toxicity is limited to transient and reversible thrombocytopenia while leucopenia plays only a minor role [4], both enabling multiple administrations after appropriate time intervals. 2. Properties of 186 Re – HEDP 2.1 Physical Properties of 186 Re Rhenium – 186 is a mainly beta – emitting radionuclide with a physical half – life of T 1/2 = 89,3 hr (3,78 d). Its main beta – emissions have maximum energies of E max,1 = 1,077 MeV (71%) and E max,2 = 0,939 MeV (22%) respectively. These energies show beta particles with short ranges in tissue, capable of delivering high doses to regions of high Re – concentrations while sparing adjacent regions thus making the irradiation well tolerated for the patient [1–3]. 1 Radiology Department, University of Athens, Aretaeio Hospital, Athens, Greece 2 Peripheral General Hospital of Nikaia, “St. Panteleimon”, Athens, Greece