ABSORBED DOSES FOR INTERNAL RADIOTHERAPY FROM 22 BETA-EMITTING RADIONUCLIDES - BETA-DOSIMETRY OF SMALL SPHERES

We calculated the mean absorbed fractions, specific absorbed fractions and mean doses per unit of cumulated activity in source spheres 10 mu m-2 cm in radius for 22 beta-emitting radionuclides potentially useful in radioimmunotherapy. We considered two models of radionuclide distr ibution, either uniform at the surface of the source or throughout its volume. For each model, we calculated both the absorbed fractions in the spherical segments composing the source and the mean absorbed frac tions. For surface distribution, we calculated the mean dose per unit of cumulated activity for a concentric sphere with a small radius (5 m um) in order to determine the minimal dose delivered to the target. Ca lculations were performed using point kernels for monoenergetic emissi ons and then integrated into the beta spectra of the different emitter s (P-32, P-33, Sc-47, Cu-67, As-77, Y-90, Rh-105, Pd-109, Ag-111, Sn-1 21, I-131, Pr-142, Pr-143, Pm-149, Sm-153, Gd-159, Ho-166, Lu-177, Re- 186, Re-188, Ir-194 and Au-199). Monoenergetic emissions were taken in to account. Results are reported in the form of tables to facilitate u se during dosimetric studies for radioimmunotherapy. An application is presented showing the potential utility of associating emitters with different energies in order to sterilize a range of tumour targets of variable size.