Combination of internal and external beam radiotherapy

External beam radiation therapy and internal vectorized radiation therapy are two types of radiothe-rapy that can be used to treat cancer. They differ in the way they are administered, and the type of radiation used. Although they can be effective in treating cancer, they each have their own advantages and disadvantages, and their combination could be synergistic. Preclinical studies on combined internal and external beam radiation therapy have mainly used radiolabelled antibodies, whose bone marrow toxicity remains the limiting factor in increasing the administered activities. The use of small radioli-gands in clinical trials has shown to be better tolerated and more effective, which explains their rapid development. The results of preclinical studies on combined internal and external beam radiation the-rapy appear heterogeneous, making it impossible to determine an ideal therapeutic sequencing scheme, and complicating the transposition to clinical studies. The few clinical studies on combined internal and external beam radiation therapy available to date have demonstrated feasibility and tolerability. More work remains to be done in the fields of dosimetry and radiobiology, as well as in the sequencing of these two irradiation modalities to optimize their combination. (c) 2023 Published by Elsevier Masson SAS on behalf of Societe franc, aise de radiotherapie oncologique (SFRO).