RADIOTOXICITY OF GADOLINIUM-148 AND RADIUM-223 IN MOUSE TESTES - RELATIVE BIOLOGICAL EFFECTIVENESS OF ALPHA-PARTICLE EMITTERS IN-VIVO

The biological effects of radionuclides that emit or particles are of considerable interest in view of their potential for therapy and their presence in the environment, The present work is a continuation of ou r ongoing effort to study the radiotoxicity of alpha-particle emitters in vivo using the survival of murine testicular sperm heads as the bi ological end point. Specifically, the relative biological effectivenes s (RBE) of very low-energy or particles (3.2 MeV) emitted by Gd-148 is investigated and determined to be 7.4 +/- 2.4 when compared to the ef fects of acute external 120 kVp X rays. This datum, in conjunction wit h our earlier results for Po-210 and Pb-212 in equilibrium with its da ughters, is used to revise and extend the range of validity of our pre vious RBE-energy relationship for a: particles emitted by tissue-incor porated radionuclides. The new empirical relationship is given by RBE, = 9.14 - 0.510 E(alpha), where 3 < E(alpha) < 9 MeV. The validity of this empirical relationship is tested by determining the RBE of the pr olific a-particle emitter Ra-223 (in equilibrium with its daughters) e xperimentally in the same biological model and comparing the value obt ained experimentally with the predicted value. The resulting RBE value s are 5.4 +/- 0.9 and 5.6, respectively. This close agreement strongly supports the adequacy of the empirical RBE-E, relationship to predict the biological effects of alpha-particle emitters in vivo. (C) 1997 b y Radiation Society.