Abstract
The natural bone seeking tendency of Ra+2, similar to the other alkali metal ions, coupled with the short range high LET of ��-particle emissions are an ideal combination for localized therapy, and recently 11.4 d 223Ra has been studied for therapy of bone tumors in rats and humans [1,2].
Actinium-225 is also an attractive radioisotope for endo-radiotherapy �� in a single decay chain from 225Ac, over 26 MeV (~70% of total) is carried by four ��- particles ranging in energy from 5.7 to 8.4 MeV [3,4]. Although Ac+3 does not home naturally to bone (rather to liver) [5,6], its parent, 225Ra (��-, t1/2 = 15 d), can be used as an in vivo source for 225Ac. A pivotal question for the 225Ra/225Ac in vivo generator system is whether translocation of the daughter nuclei occurs prior to or following the uptake of 225Ra by the bone. In order to assess potential collateral damage to soft tissue organs it is essential to quantitate the extent to which 225Ac is retained in organs following the uptake of 225Ra. We have attempted to answer these questions by investigating the extent of translocation of 225Ac and 213Bi, two daughter radioisotopes of 225Ra, following retention of initially pure 225Ra in bone in normal mice.
