HEARTS Trial for Thoracic Cancers

The goal of this clinical trial is to compare a new way of using magnetic resonance-guided adaptive radiation therapy (MRgART) to the standard of care linear accelerator (LINAC) radiation treatment in people with cancer in the thoracic region near the heart. The main question it aims to answer is whether MRgART affects the heart differently than LINAC. Participants will: * Receive radiation therapy * Undergo MRIs and bloodwork * Complete quality of life questionnaires

Inclusion Criteria: * Age \> 18 years at the time of consent. * Dosimetric eligibility criteria met using endpoints from QUANTEC (\>10% of heart receives \> 25 Gy) as determined through rapid auto-planning * Participants with histologically or cytologically proven AJCC, 8th edition including: * Stage IIB, IIIA, IIIB, IIIC, or IV non-operable non-small cell lung cancer * Limited stage small cell lung cancer, once daily treatment (excluding twice per day fractionation schemes). Stage I-III N0-2 disease esophageal/esophagogastric cancer * Stage II or III thymoma/thymic carcinoma * Other cancers in the thoracic region that meet the dosimetric and other clinical trial criteria, for example lymphoma sarcoma. * Participants must have a course of daily fractionated RT planned of at least 15 treatment fractions, typically ranging from 1.8 to 4 Gy/fraction Exclusion Criteria: * Definitive clinical or radiologic evidence of metastatic disease with life expectancy \