MULTICELLULAR DOSIMETRY FOR BETA-EMITTING RADIONUCLIDES - AUTORADIOGRAPHY, THERMOLUMINESCENT DOSIMETRY AND 3-DIMENSIONAL DOSE CALCULATIONS

Inhomogeneities in activity distributions over distances from 10 to 10 (4) mum are observed in many tumors treated with radiolabeled antibodi es. Resulting nonuniformities in absorbed dose may have consequences f or the efficacy of radioimmunotherapy. Activity variations may be dire ctly studied with quantitative autoradiography (ARG). Converting these data to absorbed dose distributions requires additional information a bout pharmacokinetics, the use of a point source function and consider ation of the complete three-dimensional activity distribution, as obta ined from sequential autoradiographic slices. Thermoluminescent dosime try with specially prepared CaSO4:Dy dosimeters implanted into tissue can directly measure absorbed dose in selected regions. The conditions under which thermoluminescent dosimeters (TLD) are used differ marked ly from ''normal'' use conditions in external beam radiotherapy. There fore special calibration and quality assurance precautions are needed to assure the precision of this technique. Procedures and pitfalls in the use of both techniques in radioimmunotherapy are described.