Within the durvalumab plus EBRT arm (cohort 2b), subjects will be enrolled in a 6+3+3 design starting at dose level 0. If < 2 out of 6 subjects experience DLT, an additional 3 subjects will be enrolled at dose level 0. If < 4 out of 9 subjects experience DLT, an additional 3 subjects will be enrolled. If < 5 out of 12 patients experience DLT, dose level 0 will be declared the RP2D for durvalumab plus EBRT. If > 2 out of 6, > 4 out of 9, or > 5 out of 12 subjects experience DLT, a RP2D will not be established and the durvalumab plus EBRT arm will not proceed to Phase 2 of the study.