Study: This research looks at using a special kind of radiation therapy called intensity-modulated proton therapy (IMPT) to treat small cell lung cancer, a type of lung cancer that grows quickly. IMPT is a newer method that targets tumors more precisely, which might cause fewer side effects.

Purpose: The study aims to find the best way to use imaging to check on the tumor during treatment and decide if any changes are needed. It will also compare the side effects, like heart problems, lung inflammation (pneumonitis), and throat inflammation (esophagitis), of IMPT to older treatments using regular radiation (photon therapy).

• **Duration:** Participation involves multiple visits over a period as advised by the oncologist.
• **Eligibility:** Adults 18+ with certain stages of small cell lung cancer who have not had overlapping radiation therapy.
• **Risks:** Possible side effects include heart, lung, and throat issues, but possibly fewer than with older treatments.