ABSORBED DOSE DISTRIBUTION OF THE AUGER EMITTERS GA-67 AND I-125 AND THE BETA-EMITTERS CU-67, Y-90, I-131, AND RE-186 AS A FUNCTION OF TUMOR SIZE, UPTAKE, AND INTRACELLULAR-DISTRIBUTION

Purpose: The influence of tumor volume, uptake of radioactive compound s in cells of tumors and normal tissues, and characteristics of the em itted ionizing particles on the efficacy of systemic radiation were st udied. Methods and Materials: The influence of these variables was ass essed using a point kernel approach combined with a distance histogram technique, Simulation calculations were performed to assess dose dist ributions for three tumor sizes (o = 200 mu m, 2 mm, or 2 cm) and six radionuclides: Ga-67, I-125, Cu-67, Y-90, I-131, and Re-186. Results: The energy deposition patterns depended on the relation of the tumor s ize and range of the emitted particles, Selective uptake was especiall y important in cases where the range was short compared to the dimensi on of the tumor. Conclusion: To attain a high dose for treatment of mi crometastases, the use of Auger and conversion electron emitters (Ga-6 7 and I-125) or beta-emitters with emission spectra including low ener getic electrons (Cu-67 and I-131) was recommended, The results demonst rated the complementary nature of selectivity of energy deposition and crossfire, This implied that for tumor cells or areas with reduced up take, crossfire from radioactivity in surrounding cells or areas with selective uptake would be provided by intermediate (conversion electro ns) or long-range (beta-particles) emissions.