Knowledge Base

Image-guided radiotherapy

During the entire radiotherapy course or during an irradiation session, anatomical variations (displacements and/or deformations) of the patient and/or the tumor area may occur. Image-guided radiotherapy is a technological improvement of the classical radiotherapy techniques that has revolutionized the discipline in the last two decades. Before its development, the patient’s positioning at the beginning of each session was based on the CT scan performed to determine the treatment plan (simulation scan) and the landmarks located on the patient’s skin, without taking into account the changes that may occur during the treatment. Nowadays, radiation therapy devices include imaging systems that allow obtaining a daily image of the region of interest to verify the positioning of the patient and of the target volume before the session. If changes are detected, the patient can be repositioned by moving the treatment table. These imaging systems are of two types:

• images produced directly via low energy irradiation of the treatment area by the linear particle accelerator that gives images similar to radiographs
• addition of a portal imaging system independent of the treatment head that allows obtaining images similar to X-ray or CT images

Recently, new treatment devices have been equipped with an MRI imaging system that allows a very precise patient’s repositioning, always with the objective of minimizing the irradiation of healthy tissues.

In image-guided radiotherapy, the patient’s repositioning during and between sessions strongly limits healthy tissue irradiation and consequently the risk of side effects. However, the additional irradiation doses delivered to the patient during imaging must be taken into account in the total dose calculation.