MR-guided proton therapy: a review and a preview

Abstract

Background: The targeting accuracy of proton therapy (PT) for moving soft-tissue tumours is expected to greatly improve by real-time magnetic resonance imaging (MRI) guidance. The integration of MRI and PT at the treatment isocenter would offer the opportunity of combining the unparalleled soft-tissue contrast and real-time imaging capabilities of MRI with the most conformal dose distribution and best dose steering capability provided by modern PT. However, hybrid systems for MR-integrated PT (MRiPT) have not been realized so far due to a number of hitherto open technological challenges. In recent years, various research groups have started addressing these challenges and exploring the technical feasibility and clinical potential of MRiPT. The aim of this contribution is to review the different aspects of MRiPT, to report on the status quo and to identify important future research topics. Methods: Four aspects currently under study and their future directions are discussed: modelling and experimental investigations of electromagnetic interactions between the MRI and PT systems, integration of MRiPT workflows in clinical facilities, proton dose calculation algorithms in magnetic fields, and MRI-only based proton treatment planning approaches. Conclusions: Although MRiPT is still in its infancy, significant progress on all four aspects has been made, showing promising results that justify further efforts for research and development to be undertaken. First non-clinical research solutions have recently been realized and are being thoroughly characterized. The prospect that first prototype MRiPT systems for clinical use will likely exist within the next 5 to 10 years seems realistic, but requires significant work to be performed by collaborative efforts of research groups and industrial partners.

MR‐guided proton therapy: Impact of magnetic fields on the detector response

“…consequently research towards online MR guidance during proton therapy is gaining momentum [29][30][31][32]. The high magnetic fields required for imaging impose additional challenges [33]. In contrast to photon-based therapy, where only secondary electrons are affected by the magnetic field, the primary particles are also affected in proton therapy [32,34,35].…”

Review of MR-Guided Radiotherapy for Esophageal Cancer

“…The ability to visualize moving soft-tissue tumors with MRI and the dosimetric advantages of the Bragg peak with proton therapy could be combined in a hybrid system for MR-integrated proton therapy (MRiPT). Although MRiPT is still in its infancy, research is currently underway to develop prototype systems for clinical use ( 49 ). In addition to MR-guided daily plan adaptation and PTV margin reduction with consequently better sparing of OARs, MRI may also provide a way to detect subclinical cardiac toxicity after CRT by visualizing areas of myocardial fibrosis and changes in ejection fraction ( 50 ).…”

X-change symposium: status and future of modern radiation oncology—from technology to biology

“…The main advantages of MR-Linac are based on the way it solves image-guided radiotherapy (IGRT) and the possibilities that this technology opens up for radiation oncology practice [15][16][17][18]. There are three main evident advantages of on board MR-Linac compared to cone beam computed tomography (CBCT) IGRT: better imaging for (1) daily positioning of the patient; (2) monitoring during treatment delivery; and (3) online adapting the treatment plan to the daily anatomy.…”