Medical physics challenges in clinical MR-guided radiotherapy

Abstract

The integration of magnetic resonance imaging (MRI) for guidance in external beam radiotherapy has faced significant research and development efforts in recent years. The current availability of linear accelerators with an embedded MRI unit, providing volumetric imaging at excellent soft tissue contrast, is expected to provide novel possibilities in the implementation of image-guided adaptive radiotherapy (IGART) protocols. This study reviews open medical physics issues in MR-guided radiotherapy (MRgRT) implementation, with a focus on current approaches and on the potential for innovation in IGART. Daily imaging in MRgRT provides the ability to visualize the static anatomy, to capture internal tumor motion and to extract quantitative image features for treatment verification and monitoring. Those capabilities enable the use of treatment adaptation, with potential benefits in terms of personalized medicine. The use of online MRI requires dedicated efforts to perform accurate dose measurements and calculations, due to the presence of magnetic fields. Likewise, MRgRT requires dedicated quality assurance (QA) protocols for safe clinical implementation. Reaction to anatomical changes in MRgRT, as visualized on daily images, demands for treatment adaptation concepts, with stringent requirements in terms of fast and accurate validation before the treatment fraction can be delivered. This entails specific challenges in terms of treatment workflow optimization, QA, and verification of the expected delivered dose while the patient is in treatment position. Those challenges require specialized medical physics developments towards the aim of fully exploiting MRI capabilities. Conversely, the use of MRgRT allows for higher confidence in tumor targeting and organs-at-risk (OAR) sparing. The systematic use of MRgRT brings the possibility of leveraging IGART methods for the optimization of tumor targeting and quantitative treatment verification. Although several challenges exist, the intrinsic benefits of MRgRT will provide a deeper understanding of dose delivery effects on an individual basis, with the potential for further treatment personalization.

Radiation-induced lung toxicity – cellular and molecular mechanisms of pathogenesis, management, and literature review

“…In the majority of cases thoracic radiotherapy represents a central part of multi-modal treatment concepts [2]. Several diagnostic and therapeutic advances, such as PETimaging [3,4], improved radiation delivery techniques [5][6][7][8][9], implementation of immunotherapy [10][11][12][13][14][15][16], and molecularly targeted therapy [17][18][19], have led to improved outcome in terms of overall survival, local and distant control as well as quality of life. However, between 10 and 30% of all patients with lung or breast cancer receiving thoracic radiotherapy develop radiation-induced pneumonitis (RIP) as a subacute treatment-associated toxicity, and they are at high risk of developing radiation-induced lung fibrosis (RILF) as late toxicity, although treatmentrelated death is uncommon [5,[20][21][22][23][24].…”

Radiomics and Dosiomics for Predicting Local Control after Carbon-Ion Radiotherapy in Skull-Base Chordoma

“…Due to the limited data available, it was not possible to separately investigate the potential confounding factors (contouring, intrinsic features reproducibility, variations in acquisition parameters) which are known to affect the computation of radiomic features [ 33 ]. Nonetheless, given the radiological relevance of chordoma appearance on MRI [ 11 ], from which haemorrhage, calcifications and other heterogeneous structures can be identified, quantitative (e.g., diffusion-weighted MRI) and standardized anatomical MR sequences (e.g., fat-saturated or contrast-enhanced) should be explored as promising sources of prognostic features [ 27 , 34 , 35 ]. Indeed, textural wavelet features from anatomical T1w- and T2w-MRI showed to be promising for SBC treated with surgery [ 28 ].…”

Magnetic resonance-guided radiation therapy: the beginning of a new era

“…In Corradini et al [1], clinical experts lay out the current clinical applicability for early adopters of MR guided radiotherapy systems, and the potential new perspectives from the technology and benefit to patients. Kurz and colleagues [2] present the technical state of the art of current systems and of MR guided adaptive radiotherapy, as well as the challenges medical physicists and engineers aim at tackling in the near future. With some delay, proton therapy has also adopted CBCT image guidance at latest generation treatment rooms.…”