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

Abstract

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 GTVTD. The median daily rigid 4D-MRI to midP-CT registration precision in patient images was <2 mm. The ATP strategy restored the target dose without increased exposure to the OARs and plan quality was independent from 3D shift distance in the range of 1–26 mm. 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.

Real‐time radial reconstruction with domain transform manifold learning for MRI‐guided radiotherapy

“…Such an approach could be adapted to assist with tracking of targets with out-of -plane motion, which represents a persistent challenge in MRI-guided radiotherapy. 59 Temporal k-space filtering, 9 optical flow techniques, 23 and neural networks tailored to radial reconstruction could also improve network performance. 57,60,61 Our results show that AUTOMAP performs well with the addition of white noise, which represents the fundamental thermal limitations to SNR in an MRI scan.…”

Towards mid-position based Stereotactic Body Radiation Therapy using online magnetic resonance imaging guidance for central lung tumours

“…In the meantime, this study demonstrates that mid-position-based treatments offer a viable dosimetric improvement over ITV-based deliveries while maintaining a 100% duty cycle. For liver SBRT, it was previously shown that a mid-position-based treatment strategy is feasible on the Unity MR-linac ( [34] ).…”

Advances in MRI‐guided precision radiotherapy

“…For example, in adaptive radiotherapy, the radiotherapy plans could be adapted based on the registration position shifts between 4D-MRI and mid-position planning. 47 In the first clinical trial for abdominal stereotactic body radiation therapy (SBRT) with 4D-MRI-based online adaptation and real-time MRI monitoring, 10 patients were treated without the aid of CT. 48 As for online treatment guidance, multiple methods have been proposed for real-time volumetric cine-MRI. on onboard 2D images to obtain 4D-MRI.…”