Image-guided radiation Therapy (IGRT)

Image-guided radiotherapy (IGRT) is a method based on the use of imaging (ionizing or non-ionizing) in the treatment room. Imaging ensures that irradiation is delivered as planned, i.e. that the planned dose distribution is precise and accurate, and is sometimes re-evaluated in the event of clinical need (adaptive radiotherapy, which de facto includes IGRT, or ART). It also makes it possible to adjust the positioning of the patient, or even the tumor, in just a few minutes, without weighing down a treatment session.

There is another, broader but less consensual definition of IGRT, which also includes imaging for tumor diagnosis and contouring of target volumes and organs at risk to prepare the irradiation plan; it could be called "image-based radiotherapy" (IBRT) rather than "guided".

The English term "IGRT" will be used, as it is much more widely used, even in France, than the French acronym.

The last twenty years have seen a veritable technological revolution in the fields of imaging and radiotherapy. Multimodality planning imaging, based on CT and one or more other modalities after registration/fusion, has considerably improved the definition of target volumes. At the same time, radiotherapy equipment has been enriched with solutions for optimizing dose conformation to target volumes using an intensity modulation principle applied to conformal radiotherapy (IMRT), or using stereotactic irradiation, or heavy ion radiotherapy.

Finally, the IGRT principle is part of a compromise on the benefit-risk ratio intrinsically linked to routine medical practice, aiming to increase the therapeutic index (reduce margins, toxicities, increase doses, local control) without making treatment unnecessarily burdensome (human and financial resources, additional patient irradiation, invasive markers, etc.). It is directly linked to demanding quality control to monitor the performance of this cutting-edge equipment.

In this article, we'll try to explain the purpose of IGRT and the various ways in which it can be applied.

Given the proliferation of irradiation modalities, and the development of technological tools adapted to radiotherapy equipment to optimize imaging during treatment, classifications...