The biodistribution of strontium was first characterized in the early 1940s. In addition to its uptake in normal bones, it was found to differentially localize in foci of active bone turnover that include tumor foci. These areas can show several fold uptake compared with normal bone. It is a fission product and pure beta emitter with an Emax beta of 1.46 MeV and a T1/2 of 50.5 days. It is handled by the body in the same manner as calcium. It is excreted via the kidneys and is taken up into the bone undergoing a "self-burial" with a long effective half-life in the skeleton and slow wash-out from blastic bone lesions (30). Lack of gamma emission precludes imaging, although attempts have been made to image the bremstrahlung (resulting in a very low quality image) or by spiking with 85Sr, the gamma emitting isotope of strontium (30). However, with a biodistribution identical to strontium isotopes, 99mTcMDP can be used as a surrogate for studying the biodistribution of 89Sr although the half-life is very different. Administration of strontium for therapy of bone metastases is based on a fixed dose scale and does not require biodistribution studies for therapy administration. Treatment doses are nonmyelosuppressive in the prescribed dose ranges (6,7).

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