Experience with the first three lung cancer patients to receive magnetic resonance (MR)-guided radiotherapy on the Elekta Unity MR-Linac in the United Kingdom (UK)

Abstract

Background: The Elekta Unity MR-Linac has been in operation at the Christie NHS Foundation Trust since May 2019. The clinical implementation of thoracic MR-guided radiotherapy has been a key objective ever since. Methods: A team of clinicians, physicists, and radiographers worked collaboratively to produce a protocol for the delivery of radical radiotherapy to patients with stage III lung cancer (Fig. 1). Results: The first lung cancer patient in the UK was treated in July 2021 and a further two patients have subsequently followed. Two patients had stage III NSCLC and the other had oligometastatic stage IV NSCLC (T4N2/3 thoracic disease and a single gluteal metastasis). The latter patient received radical radiotherapy as part of the SARON trial, including MR-guided stereotactic ablative radiotherapy to the metastasis. All three patients had bulky primary tumours in different locations within the lungs – anterior left upper lobe, posterior right upper lobe invading ribs and left upper lobe invading mediastinal pleura. The clinically available T2 3D MR sequence appeared to provide the best image resolution for all three patients. The first patient was treated with a clinician present for every fraction. However, during the treatment course of patient two, a ‘clinician-light’ approach was adopted, whereby a clinician was only contacted if dose constraints for organs at risk were found to be above a predefined level or there was clinical concern. The average couch time for each patient was 42, 50 and 45 minutes, respectively. Treatments were well tolerated and to date, no unexpected toxicities have been reported. Conclusion: Thoracic MR-guided radiotherapy using an Adapt to Position workflow has been successfully clinically implemented at the Christie NHS Foundation Trust. We aim to move to an Adapt to Shape workflow once 4D MR imaging, tracking and gating technologies are made available on the Elekta Unity.