Radiation Yield and Maximum Beta Range of Spilled Radionuclide Sr-89

Sr-89 is a new radiopharmaceutical that is now getting widespread use as part of a palliative modality against painful bone metastasis. There are also recent clinical trials employing it as adjuvant agent concommitant with chemotherapy for a systemic attack at metastatic spread of primary lesions. The physiologic and metabolic mechanism for organ incorporation and excretion of this radionuclide mimics that of the body mineral calcium and there is a big preferential affinity towards lytic lesions in the bone as opposed to normal organ tissues. The radiation safety aspect of Sr-89 appears simple because as a pure beta-emitter, it has a maximum tissue range of only 8 mm. However, special precaution is needed in case of spills, as this radionuclide can easily contaminate any absorbent material worn by therapy personnel and other materials inside the treatment or exam room. State regulations usually require storage of 10 half-lives, so that these contaminants need keeping for 1.5 years. Also, although the beta range is short, the range of Bremmstrahlung photon produced by the betas in air could be substantial. The aim of this work is to address these questions of maximum range and radiation yield of both betas and Bremsstrahlung photons in case of a spilled Sr-89. Using the analytical ansatz of Bethe-Heitler, we arrive at the beta range of 37 cm and radiation yield of 0.7%. The energy emission by Bremmstrahlung is 1.6 (106) Mev/sec with a photon fluence rate at 1 m of 8.7 photons/cm2-sec. Comparison with Monte Carlo simulation is underway