The effectiveness of targeted radionuclide therapy (TRT) is well-recognized for certain cancers. However, in order to maximize the tumor dose, minimize potential toxicity in critical organs, and monitor the treatment effects, it is preferred to perform the patient-specific internal dosimetry based on their own medical data. As compared to the conventional 2D planar imaging technique, quantitative 3D imaging methods, especially SPECT, PET and bremsstrahlung imaging, can provide the spatial distribution of TRT theranostic tracers on a voxel level with improved quantitative accuracy. Following quantitative imaging, the use of a streamline 3D dosimetric software with functions of volume-of-interest segmentation, image registration, time-activity-curve fitting and dose conversion is essential to assess the 3D tumor and critical organ absorbed dose distribution for clinical practice.