Despite a rise in clinical use of radiopharmaceutical therapies, the biological effects of radionuclides and their relationship with absorbed radiation dose are poorly understood. Here, we set out to define this relationship for Auger electron-emitters [99mTc]TcO4 and [123I]I, and β--particle-emitter [188Re]ReO4. Studies were carried out using genetically-modified cells that permitted direct radionuclide comparisons. Triple-negative MDA-MB-231 breast cancer cells, expressing the human sodium/iodide symporter (hNIS) and green fluorescent protein (GFP; MDA-MB-231.hNIS-GFP) were used. In vitro radiotoxicity of [99mTc]TcO4, [123I]I and [188Re]ReO4 was determined using clonogenic assays. Radionuclide uptake, efflux, and subcellular location were used to calculate nuclear-absorbed doses using the Medical Internal Radiation Dose formalism. In vivo studies were performed using female NSG mice bearing orthotopic MDA-MB-231.hNIS-GFP tumors and compared to X-ray-treated (12.6-15 Gy) and untreated cohorts. Absorbed dose per unit activity in tumors and NIS-expressing organs were extrapolated to reference human adult models using OLINDA/EXM®. [99mTc]TcO4- and [123I]I reduced the survival fraction only in hNIS-expressing cells, whereas [188Re]ReO4 reduced survival fraction in hNIS-expressing and parental cells. [123I]I required 2.4-fold and 1.5-fold lower decays/cell to achieve 37% survival compared to [99mTc]TcO4- and [188Re]ReO4, respectively, following 72 hours incubation. Additionally, [99mTc]TcO4-, [123I]I and [188Re]ReO4 had superior cell killing effectiveness in vitro compared to X-rays. In vivo, X-ray led to a greater median survival compared to [188Re]ReO4 and [123I]I (54 days versus 45 and 43 days, respectively). Unlike the X-ray cohort, no metastases were visualized in the radionuclide-treated cohorts. Extrapolated human absorbed doses of [188Re]ReO4 to a 1 g tumor were 13.8-fold and 11.2-fold greater than for [123I]I in female and male models, respectively. This work reports reference dose-effect data using cell and tumor models for [99mTc]TcO4, [123I]I, and [188Re]ReO4, for the first time. We further demonstrate the tumor controlling effects of [123I]I, and [188Re]ReO4 in comparison to EBRT.