Master protocol trial design for technical feasibility of MR-guided radiotherapy

The use of master protocols for efficient trial design to evaluate radiotherapy interventions: a systematic review

The aim of this review was to highlight why the use of master protocols trial design is particularly useful for radiotherapy intervention trials where complex setup pathways (including quality assurance, user training, and integrating multiple modalities of treatment) may hinder clinical advances. We carried out a systematic review according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, reviewing the findings using a landscape analysis. Results were summarized descriptively, reporting on trial characteristics highlighting the benefits, limitations, and challenges of developing and implementing radiotherapy master protocols, with three case studies selected to explore these issues in more detail. Twelve studies were suitable for inclusion (4 platform trials, 3 umbrella trials, and 5 basket trials), evaluating a mix of solid tumor sites in both curative and palliative settings. The interventions were categorized into 1) novel agent and radiotherapy combinations; 2) radiotherapy dose personalization; and 3) device evaluation, with a case study provided for each intervention. Benefits of master protocol trials for radiotherapy intervention include protocol efficiency for implementation of novel radiotherapy techniques; accelerating the evaluation of novel agent drug and radiotherapy combinations; and more efficient translational research opportunities, leading to cost savings and research efficiency to improve patient outcomes. Master protocols offer an innovative platform under which multiple clinical questions can be addressed within a single trial. Due to the complexity of radiotherapy trial setup, cost and research efficiency savings may be more apparent than in systemic treatment trials. Use of this research approach may be the change needed to push forward oncological innovation within radiation oncology.

Technical feasibility and clinical evaluation of 4D-MRI guided liver SBRT on the MR-linac

PURPOSE

Image-guided stereotactic body radiation therapy (SBRT) is an important local treatment for liver metastases. MRI-guidance enables direct tumor visualization, eliminating fiducial marker implantation. The purpose of this study was to test technical feasibility of our 4D-MRI guided liver SBRT workflow. Additionally, intra-fraction target motion and consequent target-coverage were studied.

MATERIALS&METHODS

Patients with liver metastases were included in this sub-study of the prospective UMBRELLA clinical trial. Patients received mid-position (midP) SBRT. The daily adapt-to-position workflow included localization, verification and intra-fraction tumor midP monitoring using 4D-MRI. Technical feasibility was established based on persistence of the treatment protocol, treatment time ≤1 hour, no geographical miss and no unexpected acute toxicity grade >3. All 4D-MRIs were registered to the planning midP-CT and tumor midP and amplitude were calculated. Additionally, delivered target dose was accumulated incorporating the 4D-MRI intra-fraction tumor motion and evaluated with Monte-Carlo error simulations.

RESULTS

20 patients with liver metastases were included and treated with 4D-MRI guided SBRT. Feasibility criteria were met in all-but-one patient. No grade ≥3 acute toxicity was observed. Group mean (M), systematic and random midP-drifts were 2.4mm, 2.6mm and 3.1mm in CC-direction. 4D-MRI tumor CC-amplitudes were reduced compared to the simulation 4D-CT (M=-1.9mm) and decreased during treatment (M=-1.4mm). Dose accumulation showed adquate target-coverage on a population level.

CONCLUSION

We successfully demonstrated technical feasibility of 4D-MRI guided SBRT in a cohort of 20 patients with liver metastases. However, substantial midposition drifts occurred which stress the need for intra-fraction motion management strategies to further increase the precision of treatment delivery.