Thymoma and Thymic Carcinoma Stage II-III

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