Dose accumulation for MR-guided adaptive radiotherapy: From practical considerations to state-of-the-art clinical implementation

Abstract

MRI-linear accelerator (MR-linac) devices have been introduced into clinical practice in recent years and have enabled MR-guided adaptive radiation therapy (MRgART). However, by accounting for anatomical changes throughout radiation therapy (RT) and delivering different treatment plans at each fraction, adaptive radiation therapy (ART) highlights several challenges in terms of calculating the total delivered dose. Dose accumulation strategies—which typically involve deformable image registration between planning images, deformable dose mapping, and voxel-wise dose summation—can be employed for ART to estimate the delivered dose. In MRgART, plan adaptation on MRI instead of CT necessitates additional considerations in the dose accumulation process because MRI pixel values do not contain the quantitative information used for dose calculation. In this review, we discuss considerations for dose accumulation specific to MRgART and in relation to current MR-linac clinical workflows. We present a general dose accumulation framework for MRgART and discuss relevant quality assurance criteria. Finally, we highlight the clinical importance of dose accumulation in the ART era as well as the possible ways in which dose accumulation can transform clinical practice and improve our ability to deliver personalized RT.

Structure-specific rigid dose accumulation dosimetric analysis of ablative stereotactic MRI-guided adaptive radiation therapy in ultracentral lung lesions

“…Determining the true cumulative dose delivered is difficult 35 . A common technique is the use of deformable image registration (DIR).…”

Evaluation and mitigation of deformable image registration uncertainties for MRI‐guided adaptive radiotherapy

“…One‐tailed Wilcoxon‐Mann‐Whitney (WMW) tests 17 were programmed with Excel for Microsoft 365 (Microsoft Corporation, Redmond, Washington) to determine the statistical significance of FEM improvements. The thresholds of 3 mm in MDA and 0.8 in DSC were used to evaluate DIRs at organ boundaries, 4 and the range from 0.8 to 1.2 for JD was utilized for evaluation of DIRs in soft tissue regions. 8 It is important to note that JD values could fall outside that range if an organ undergoes significant volume changes.…”

“… 1 Various techniques have been developed to streamline the adaptation process, including auto‐segmentation, 2 real‐time MR imaging, 3 and deformable dose accumulation (DDA). 4 DDA relies on deformable image registration (DIR) techniques to derive displacement vector fields that can be used to transfer doses from daily MR images to a consensus image for dose comparison or assessment. 5 Several factors could compromise MRI registrations.…”

“… 8 These evaluation metrics, coupled with their clinical tolerances, provide valuable guidance for clinical practice. 4 However, when registration errors exceed acceptable clinical thresholds, rectifying these errors becomes paramount. In contrast to image‐based registration algorithms, which are susceptible to adverse image characteristics such as imaging artifacts and low image contrasts, 9 mechanical modeling techniques, being independent of such characteristics, present a promising avenue for mitigating errors in image‐based registrations.…”

Clinical introduction of MR-guided radiotherapy for esophageal cancer

“…If this can be done safely, hypofractionation becomes a possibility to improve efficiency of esophageal cancer treatments. Furthermore, real-time cine-MR imaging could be used to reconstruct the delivered dose and used as feedback in subsequent treatment fractions to optimize target coverage [143]. Similarly, additional functional imaging, such as DWI and DCE imaging, during a MRgRT treatment period could potentially predict the impact of the treatment (Figure 7.1) [87,112,144].…”