Lecture 6: Organ Motion Matters, Bernt Nordin, Lioness
Some experiences from the first four years of clinical use of adaptive 4D MRI-guided radiotherapy.
An update.

Bernt Nordin1, Charlotta Nordin1

1 LIONESS Therapeutics AB, Stockholm, Sweden

Background: Adaptive MRI-guided radiotherapy using the ViewRay MRIdian system is in routine clinical practice at nine institutions in the world and the number is growing. A wide range of disease sites have been treated with enhanced soft tissue visualization, improving the dose delivery accuracy and allowing for smaller margins. Soft tissue visualizations with online MR cine before and during treatment have helped clinicians to better understand the impact of organ motion in radiotherapy and the need for daily adaptive re-optimization of treatment plans. The second-generation MRIdian system with a linear accelerator is now introduced in clinical practice.

Purpose:  To illustrate the paradigm shift which is occurring in radiotherapy with the introduction of online MRI guidance for adaptive radiotherapy.

Materials and Methods:  Commercially available MR-IGRT systems4 consisting of a combination of 4D MRI, Monte Carlo TPS and rotating radiation delivery apparatus have now been in clinical use for 3,5 years. We summarize information presented by physicians and physicists at ESTRO, ASTRO and AAPM for a variety of disease sites where the technology provided improved visualization, tracking and re-planning capabilities to significantly improve the accuracy of dose deliveries.

Results: For a number of disease sites the clinical practice have changed. On-line tumor and OAR tracking with continuously updating MR images have allowed smaller margins around the target with less normal tissue in the field. Patient setup and internal organ localization have improved. All treatments are in practice becoming stereotactic and 4D adaptive with on-line soft-tissue visualization during radiation, which is a first in the history of radiation therapy. Multi-institutional clinical studies are now underway to determine how patient outcomes are improved, in for instance pancreatic cancer.

Conclusion: Organ motion matters and the ability to see what we treat help clinicians improve the practice of radiotherapy and ultimately patient outcomes.

4MRIdian systems and MRIdian Linac systems from ViewRay Inc., USA

Presenting author: bernt.nordin@lightions.com