Practical guidance in the use of image-guided radiotherapy systems

From mega-voltage portal images acquired on an electronic system (EPID), technological research has developed 3D and recently 4D volumetric verification modalities, allowing a direct visualization of the target, a direct comparison with the planning-TC and an optimization of the treatment (reduction of set-up errors, verification of the need for re-planning), leading to the very modern Image Guided RadioTherapy (IGRT). IGRT allows different technical solutions through direct or indirect visualization of the tumor and the acquisition of pre-treatment verification images, allowing to identify, quantify and correct errors related to set-up and organ-tumor motion, obtaining a greater compliance of the delivered dose, decreasing the risk of "geographic miss" and toxicity to healthy tissues and reducing the margins from CTV to PTV for the implementation of "dose escalation" protocols.