Primary Objective:~Stage I: Assess the feasibility of SMART for central lung tumors with simulated online adaptive planning.~Stage II: Evaluate the feasibility and safety of SMART in central lung tumors treated with 50Gy in 4-5 fractions.~Secondary Objectives:~Stage I: Determine clinical features that predict for greater benefit from adaptive planning Stage I: Determine the potential dosimetric benefit of SMART for central lung tumor Stage II: Determine the safety and efficacy of SMART for central lung tumors treated with 50Gy in 4-5 fractions.~Exploratory objectives:~Validate cine imaging and motion management strategies on the MR-linac
To learn if using MRI (magnetic resonance imaging) to guide radiation therapy can help to control central lung cancer. The results of the MRI-guided radiation therapy will be compared to conventional radiation therapy (guided by CT scans) during this study.