All subjects receiving durvalumab + EBRT will begin radiation therapy within 56 days following the TURBT. Radiation therapy will consist of three individual 6 Gy fractions planned approximately on Days 1, 3, and 5 of Cycle 1 only. To accommodate regional variations in the proximity and scheduling complexities of multi-disciplinary clinics required for therapy, radiation therapy may be delivered on Day 1 ± 1 day and Day 3 ± 1 day provided the Day 1 and Day 3 fractions are separated by 1 day. Similarly, radiation therapy may be delivered on Day 5 ± 2 days provided the Day 3 and Day 5 fractions are separated by 1 day. This will give a total dose to the gross bladder of 18 Gy. Simulation and treatment on the same day is permitted. The overall schema is for small field pelvic irradiation given by 3D conformal irradiation to the entire bladder and prostatic urethra (in men). No radiation dose reductions are planned.