MRI-guided linear accelerator

SHORT VERSION

The MRI-guided linear accelerator is a radiation therapy device in which images are acquired by an embedded MRI, not a CT, scanner. Compared with CT, MRI provides higher definition images, particularly of soft tissue tumors, and allows the exact tumor delineation to deliver the right amount of radiation to the patient. Moreover, the anatomical changes of the tumor or nearby organs can be taken into account before each session and the tumor motion can be monitored during irradiation in real time.

The MRI-guided linear accelerator is a radiotherapy device that combines a linear accelerator and a MRI system to offer cancer treatment with an extremely high degree of precision. Thanks to its on-board MRI system, this device can take into account the anatomical changes of the tumor and nearby organs before each session and monitor the tumor during irradiation in real time. The device can be used for conformal radiotherapy with intensity modulation and for stereotactic radiotherapy. Currently, two systems are available: MRIdianⓇ from Viewray and UnityⓇ from Elekta.

This system allows clinicians:

  • to acquire images with higher definition, compared with CT, by visualizing in soft tissues the exact tumor contours using MRI;
  • to continuously monitor the tumor volume by MRI during treatment: the treatment beam is activated only if the tumor position is correct (i.e. only when the tumor is within the predefined “acceptable” limits);
  • to adapt the treatment plan on a daily basis if necessary. If the anatomical modifications are too important, the initial plan is no longer adapted and the way of delivering the dose must be calculated again to ensure the specific irradiation of the tumor and healthy tissue sparing (i.e. adaptive radiotherapy)

The MRI-guided linear accelerator is particularly suitable for mobile tumors, such as pancreatic, liver, prostate or lung tumors.

Finally, unlike other imaging devices, MRI provides images without delivering any additional radiation dose to the patient.