Dosimetric principles of targeted radiotherapy and radioimmunotherapy

The use of radioisotopes in therapy represents a field of application that is constantly increasing. Therapy applications in nuclear medicine are expected to reach 40% of clinical activity in the 2020–2030 decade. Radionuclide therapy can be delineated into two main categories. The first approach uses the inherent biodistribution properties of the radionuclide, whereby it naturally accumulates in cancerous tissue. For example, radium-223 is a calcium-mimetic isotope incorporated in sites of increased bone turnover and osteoblastic activity. The second approach prefers the conjugation of the radionuclide to vectors such as monoclonal antibodies (mAbs), peptides, or small molecules to target tumor-associated antigens, allowing the possibility to treat a wide range of neoplastic pathologies. In principle, as is proper practice for therapeutic regimes with ionizing radiation, a dosimetric approach should be performed to optimize and personalize the treatment. The dosimetry of the lesion may be more effective in order to adapt and maximize the beneficial effects of the treatment.