Simple SummaryThe sentinel lymph node is a surgical technique developed in oncological surgery to identify and analyze fewer lymph nodes than a conventional lymph node dissection in order to limit the morbidity and mortality of such an extensive procedure without compromising the patients’ outcomes. This concept seems to also be useful in radiation oncology that treats lymph node areas. This may help radiation oncologists to treat their patients more precisely by targeting more accurately pathological sites and sparing healthy tissues. The aim of this review is to highlight the feasibility and level of proof regarding the use of this technique for treatment planning in radiation oncology.AbstractThe sentinel lymph node technique is minimally invasive and used routinely by surgeons, reducing the need for morbid extensive lymph node dissections, which is a significant advantage for cancer staging and treatment decisions. The sentinel lymph node could also help radiation oncologists to identify tumor drainage for each of their patients, leading to a more personalized radiotherapy, instead of a probabilistic irradiation based on delineation atlases. The aim is both to avoid recurrence in unexpected areas and to limit the volume of irradiated healthy tissues. The aim of our study is to evaluate the impact of sentinel lymph node mapping for radiation oncologists. This concept, relying on sentinel lymph node mapping for treatment planning, is known as lymph-flow-guided radiotherapy. We present an up-to-date narrative literature review showing the potential applications of the sentinel lymph node technique for radiotherapy, as well as the limits that need to be addressed before its routine usage.