4.6 Article

Validation of a 4D-MRI guided liver stereotactic body radiation therapy strategy for implementation on the MR-linac

期刊

PHYSICS IN MEDICINE AND BIOLOGY
卷 66, 期 10, 页码 -

出版社

IOP Publishing Ltd
DOI: 10.1088/1361-6560/abfada

关键词

4D-MRI; MR-linac; IGRT; Liver SBRT; Adaptive radiotherapy

资金

  1. Elekta AB (Stockholm, Sweden)

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The 4D-MRI guided strategy demonstrated excellent performance in all workflow tests, including 4D-MRI scanning, tumor registration with CT images, calculation of daily tumor mid-position misalignment, plan adaptation, and adapted plan delivery, in preparation for clinical introduction on the Unity MR-linac.
Purpose. Accurate tumor localization for image-guided liver stereotactic body radiation therapy (SBRT) is challenging due to respiratory motion and poor tumor visibility on conventional x-ray based images. Novel integrated MRI and radiotherapy systems enable direct in-room tumor visualization, potentially increasing treatment accuracy. As these systems currently do not provide a 4D image-guided radiotherapy strategy, we developed a 4D-MRI guided liver SBRT workflow and validated all steps for implementation on the Unity MR-linac. Materials and Methods. The proposed workflow consists of five steps: (1) acquisition of a daily 4D-MRI scan, (2) 4D-MRI to mid-position planning-CT rigid tumor registration, (3) calculation of daily tumor midP misalignment, (4) plan adaptation using adapt-to-position (ATP) with segment-weights optimization and (5) adapted plan delivery. The workflow was first validated in a motion phantom, performing regular motion at different baselines (+/- 5 to +/- 10 mm) and patient-derived respiratory signals with varying degrees of irregularity. 4D-MRI derived respiratory signals and 4D-MRI to planning CT registrations were compared to the phantom input, and gamma and dose-area-histogram analyses were performed on the delivered dose distributions on film. Additionally, 4D-MRI to CT registration performance was evaluated in patient images using the full-circle method (transitivity analysis). Plan adaption was further analyzed in-silico by creating adapted treatment plans for 15 patients with oligometastatic liver disease. Results. Phantom trajectories could be reliably extracted from 4D-MRI scans and 4D-MRI to CT registration showed submillimeter accuracy. The DAH-analysis demonstrated excellent coverage of the dose evaluation structures GTV and GTV(TD). The median daily rigid 4D-MRI to midP-CT registration precision in patient images was Conclusions. The proposed 4D-MRI guided strategy showed excellent performance in all workflow tests in preparation of the clinical introduction on the Unity MR-linac.

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