Developments in the internal dosimetry of radiopharmaceuticals

Various radionuclides are used in nuclear medicine in different diagnostic and therapeutic procedures. Recently, interest has grown in therapeutic agents for some interesting applications in nuclear medicine. Internal dose models and methods in use for many years are well established, and can give radiation doses to stylised models representing reference individuals. Kinetic analyses need to be carefully planned, and dose conversion factors that are most similar to the subject in question should be chosen, which can then be tailored somewhat to be more patient-specific. Internal dose calculations, however, are currently not relevant in patient management in internal emitter therapy, as they are not sufficiently accurate or detailed to guide clinical decision-making, and as calculated doses have historically not been well correlated with observed effects on tissues. Great strides are being made at many centres regarding the use of patient image data to construct individualised voxel-based models for more detailed and patient-specific dose calculations, and new findings are encouraging regarding improvement of internal dose models to provide better correlations of dose and effect. These recent advances make it likely that the relevance will soon change to be more similar to that of external beam treatment planning.