3-DIMENSIONAL DOSIMETRY FOR RADIOIMMUNOTHERAPY TREATMENT PLANNING

Absorbed-dose calculations for radioimmunotherapy are generally based on tracer imaging studies of the labeled antibody. Such calculations y ield estimates of the average dose to normal and target tissues assumi ng idealized geometries for both the radioactivity source volume and t he target volume. This work describes a methodology that integrates fu nctional information obtained from SPECT or PET with anatomical inform ation from CT or MRI. These imaging modalities are used to define the actual shape and position of the radioactivity source volume relative to the patient's anatomy. This information is then used to calculate t he spatially varying absorbed dose, depicted in ''colorwash'' superimp osed on the anatomical imaging study. By accounting for individual upt ake characteristics of a particular tumor and/or normal tissue volume and superimposing resulting absorbed-dose distribution over patient an atomy, this approach provides a patient-specific assessment of the tar get-to-surrounding normal tissue absorbed-dose ratio. Such information is particularly important in a treatment planning approach to radioim munotherapy, wherein a therapeutic administration of antibody is prece ded by a tracer imaging study to assess therapeutic benefit.