In:
Medical Physics, Wiley
Abstract:
T 2 * mapping can characterize tumor hypoxia, which may be associated with resistance to therapy. Acquiring T 2 * maps during MR‐guided radiotherapy could inform treatment adaptation by, for example, escalating the dose to resistant sub‐volumes. Purpose The purpose of this work is to demonstrate the feasibility of the accelerated T 2 * mapping technique using model‐based image reconstruction with integrated trajectory auto‐correction (TrACR) for MR‐guided radiotherapy on an MR‐Linear accelerator (MR‐Linac). Materials and methods The proposed method was validated in a numerical phantom, where two T 2 * mapping approaches (sequential and joint) were compared for different noise levels (0,0.1,0.5,1) and gradient delays ([1, ‐1] and [1, ‐2] in units of dwell time for x‐ and y‐axis, respectively). Fully sampled k‐space was retrospectively undersampled using two different undersampling patterns. Root mean square errors (RMSEs) were calculated between reconstructed T 2 * maps and ground truth. In vivo data was acquired twice weekly in one prostate and one head and neck cancer patient undergoing treatment on a 1.5 T MR‐Linac. Data were retrospectively undersampled and T 2 * maps reconstructed, with and without trajectory corrections were compared. Results Numerical simulations demonstrated that, for all noise levels, T 2 * maps reconstructed with a joint approach demonstrated less error compared to an uncorrected and sequential approach. For a noise level of 0.1, uniform undersampling and gradient delay [1, ‐1] (in units of dwell time for x‐ and y‐axis, respectively), RMSEs for sequential and joint approaches were 13.01 and 9.32 ms, respectively, which reduced to 10.92 and 5.89 ms for a gradient delay of [1, 2] . Similarly, for alternate undersampling and gradient delay [1, ‐1], RMSEs for sequential and joint approaches were 9.80 and 8.90 ms, respectively, which reduced to 9.10 and 5.40 ms for gradient delay [1, 2] . For in vivo data, T 2 * maps reconstructed with our proposed approach resulted in less artifacts and improved visual appearance compared to the uncorrected approach. For both prostate and head and neck cancer patients, T 2 * maps reconstructed from different treatment fractions showed changes within the planning target volume (PTV). Conclusion Using the proposed approach, a retrospective data‐driven gradient delay correction can be performed, which is particularly relevant for hybrid devices, where full information on the machine configuration is not available for image reconstruction. T 2 * maps were acquired in under 5 min and can be integrated into MR‐guided radiotherapy treatment workflows, which minimizes patient burden and leaves time for additional imaging for online adaptive radiotherapy on an MR‐Linac.
Type of Medium:
Online Resource
ISSN:
0094-2405
,
2473-4209
Language:
English
Publisher:
Wiley
Publication Date:
2023
detail.hit.zdb_id:
1466421-5
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