MRI guided radiotherapy

Abstract

Magnetic Resonance Imaging (MRI) has been a part of radiation therapy for many years, but its role is expanding. MR provides soft tissue contrast that is superior to what can be obtained with computed tomography (CT), the modality used most often to support radiation therapy treatment simulation. There are a number of critical challenges to employing MR for simulation imaging, namely the reduced spatial fidelity, and the lack of a direct relationship between MR image values and electron density, a quantity needed for dose calculations, as well as a difference between MR image values and the attenuation of kV X-rays, used to aid in patient positioning. These challenges are being met by clinics and companies, to the extent that the exclusive use of MR for simulation is now possible in a number of treatment sites. While MR has been used for simulation, it has only recently been introduced into the treatment room. Integrating MR with patient positioning and monitoring before and during treatment, respectively, would potentially improve radiation therapy treatment accuracy, enabling tighter uncertainty margins and ultimately improving outcomes. The challenges of integrating a MRI system with radiation treatment delivery have been recently met by radiation therapy equipment manufacturers, providing the radiation oncology community with an opportunity to deliver radiation doses with unparalleled accuracy.