Group 1: People in this group will get the usual chemotherapy and radiation treatment for this cancer. They will have radiation 5 days a week for 4 to 5 weeks. That means about 20 treatments in total.

Group 2: People in this group will get the usual chemotherapy and a new way of giving radiation. This way uses fewer treatments with a higher dose. They will have radiation up to 2 days a week for up to 4 weeks. That means about 5 treatments in total.

This study wants to see if a very short radiation treatment works at least as well as a longer radiation treatment for bladder cancer. The main goal is to show that the shorter treatment is not worse than the longer one when keeping the bladder healthy and free of major problems for three years.

The study will also compare side effects that affect peeing and bowel movements, how patients feel and report their health, and how long people stay healthy without the cancer getting worse or spreading. It will look at overall survival too.

Researchers will study special signs in the blood and urine, called biomarkers, to see if they can tell whether the cancer might come back. These include ctDNA, tissue-free minimal residual disease, and urine tumor DNA. They will also check these signs when the cancer gets worse to see if they show the disease is present.

To join this study, patients must have bladder cancer proven by a lab test. The cancer must be in stages called cT2 to T3 and must not have spread to the lymph nodes or other parts of the body. Before joining, patients need a surgery called TURBT to remove as much of the tumor as possible.

Patients also need scans of the chest, belly, and pelvis using CT or MRI to make sure the cancer has not spread. If any lymph nodes look big, they must be tested to show there is no cancer. Patients cannot have cancer that has spread or certain types of bladder cancer.

Patients must be 18 or older. They cannot have had radiation to the pelvis before. If they had other treatments, any side effects must be mostly gone.

The purpose of this study is to compare two ways of giving radiation along with the usual chemotherapy. One way gives a higher dose each time but fewer treatments in a shorter time. The other way gives a lower dose each time but more treatments over a longer time. Both ways give the same total amount of radiation. The shorter treatment might help you keep your bladder and stop the cancer from coming back or spreading.