Standard radiation planning aims to optimize dose to the anatomic lung volume, without consideration of the differences in regional lung function. Functional lung avoidance radiotherapy aims to reduce radiotherapy dose to regions of functioning lung, instead depositing dose in areas of lung that are not well-ventilated. Functional lung regions are determined using noble-gas MRI and co-registered to the radiotherapy planning CT scans. Functional lung avoidance radiotherapy has been demonstrated to be feasible, and this trial aims to compare outcomes between standard radiotherapy (with concurrent chemotherapy) vs. functional lung avoidance radiotherapy (with concurrent chemotherapy).