Abstract
Rhenium-186 (Re-186) is a β-emitting radionuclide. Emitted β-particles have ranges up to 4.5 mm in tissue, capable of delivering high doses to skeletal regions of high Re-186 concentrations while sparing adjacent radiosensitive regions and thus making the irradiation well tolerated for the patient. Along with the β-emissions, γ-rays are emitted having an adequate energy for imaging during therapy and biodistribution assessment for patient-specific dosimetry calculations. The relatively short physical half-life combined with the β-emissions allows the delivery of relatively high activity rate for a short period of time in areas of concentration. This study is a short review concerning the palliative treatment of skeletal metastases using 186Re-HEDP. After presenting the dominant ways of 186Re production, special emphasis is given to dosimetry issues while the effect of palliation therapy can be evaluated through the comparison of the absorbed dose in metastatic lesion relatively to the normal bone region. Accurate dose estimation is required taking into account the anatomic individual difference of each patient. For this purpose a patient specific dosimetric model considering metastatic lesions as spherical nodules is introduced. In order to quantify in a representative way the results of palliation treatment, the concept of therapeutic ratios is analyzed.
Highlights
MO), is widely used for palliative treatment of bone metastases originating from breast or prostate cancer
Re-186 palliative treatment is recommended to patients with persisting bone pains after chemotherapy or external beam therapy and having life expectancy at least 6 months
In other studies the pain response and hematologic toxicity between single and multiple therapies with 186Re-HEDP under zoledronic acid in patients suffering from painful osseous metastases from prostate or breast cancer were investigated, whereas the predictive value of various bone formation and resorption markers in patients with bone metastases from prostate cancer after palliative treatment with 186Re-HEDP was evaluated [18,19,20]
Summary
Re-186 can be produced either at a nuclear reactor or at a particle accelerator (cyclotron). The thermal and epithermal cross-sections for neutron capture are high (106 and 1632 barns, resp.), the specific activity of Re-186 required for antibody labeling is hardly achieved using low neutron flux reactors. It is marginally sufficient for preparation of phosphonates for palliative treatment of bone pain from osseous metastases. Cyclotrons have the unique ability of producing radionuclides that decay by electron capture or positron emission, in non-carrieradded form. In this case, Re-186 is produced mainly via proton bombardment of natural tungsten W-186 as target, 186W(p, n) 186Re or 186W(d, 2n) 186Re [3]. Re-186 89.3 h W-186 (7.5%) Os-186 (92.5%) 346,7 keV 1077 keV (71%) 939 keV (22%) 137 keV (9%) 4.5 mm (average 1.1 mm)
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