This study is investigating a new treatment for non-muscle invasive bladder cancer. It compares **pembrolizumab**, a type of immunotherapy, combined with radiation therapy to the usual chemotherapy drugs like cisplatin and gemcitabine along with radiation. **Immunotherapy** helps your immune system fight cancer, while **chemotherapy** uses drugs to kill or stop cancer cells from spreading. **Radiation therapy** uses high-energy rays to kill cancer cells. **Key Points:** - The study involves random assignment to one of two groups: one receiving chemotherapy and radiation, the other receiving pembrolizumab and radiation. - Participation requires multiple visits for treatments and follow-ups over several years. - There are potential side effects, and the study aims to compare how well each treatment works in keeping the bladder cancer-free. Participants must meet specific health criteria, be over 18, and not have certain health issues or prior treatments. After treatment, follow-ups occur every few months for the first two years, then less frequently for up to five years. This trial could lead to better treatment options for bladder cancer in the future.