Magnetic resonance-guided radiotherapy (MRgRT) for patients with lung cancer

Abstract

Background: Magnetic resonance-guided radiotherapy (MRgRT) offers improved soft tissue contrast, the ability to gate and track tumours and the option of adapting treatment daily to compensate for changing target volumes or anatomy (Sim et al., 2020). It may help to improve the therapeutic index of radiotherapy treatment for lung cancer thereby improving outcomes for patients, whose outcomes generally remain poor. Its implementation and use is not without its challenges, however. Method: An updated literature search on PubMed in January 2021 identified relevant papers. We also received personal correspondence from clinicians who have had experience with MRgRT in the lung cancer setting. Treatments on the ViewRay MRIdian or the Elekta Unity radiotherapy machines were reviewed. Results: Several centres around the world have now treated patients with lung cancer with MRgRT (Crockett et al., 2021). Most of the treatments were delivered on the MRIdian and involved the use of stereotactic ablative radiotherapy for early-stage or oligometastatic disease, including (ultra-) central tumours. The majority of centres adapted treatments daily based on anatomical changes. Low rates of severe toxicity (0-8% ≥ grade 3) have been reported and preliminary outcome data appears favourable. Technical issues relating to MRgRT treatment in lung cancer have been highlighted, including challenges relating to image quality, the magnetic field’s effect on dose distribution and accounting for both physiological respiratory and cardiac motion. Conclusion: The use of MRgRT for patients with lung cancer is still in its infancy. Long-term toxicity data is currently lacking. Future studies will focus on addressing technical issues surrounding its use and the feasibility of treating patients with stage III disease using adaptive RT, as this group is likely where the advantages of MRgRT may be best exploited. The first UK patient with lung cancer will be treated on a Unity MR-linac in April 2021.