Study of Radiation Therapy Followed by Atezolizumab in Stage II or III Non-small Cell Lung Cancer Patients

Inclusion Criteria: * REGISTRATION STEP 1: Participants must have pathologic (cytological or histological) proof of non-small cell lung cancer (NSCLC) * REGISTRATION STEP 1: Participants must have stage III NSCLC with Zubrod performance status of 2 or stage II NSCLC with Zubrod performance status of 0-2 * REGISTRATION STEP 1: Participants must not be candidates for surgical resection in the opinion of the treating investigator. Participants whose disease was previously resected must have experienced local or regional recurrence at least 12 months after resection * REGISTRATION STEP 1: Participants must not be candidates for concurrent chemoradiation in the opinion of the treating investigator * REGISTRATION STEP 1: Participants must have measurable or non-measurable disease documented by CT or MRI. Measurable disease must be assessed within 28 days prior to Registration Step 1. Non-measurable disease must be assessed within 42 days prior to Step 1 registration. The CT from a combined positron emission tomography (PET)/CT may be used only if it is of diagnostic quality. All known sites of disease must be assessed and documented on the Baseline Tumor Assessment Form (RECIST 1.1) * REGISTRATION STEP 1: Participants must have an MRI or CT scan of the brain with contrast within 28 days prior to Registration Step 1 * REGISTRATION STEP 1: Participants' disease must fit within the radiation constraints in the opinion of a local radiation oncologist * REGISTRATION STEP 1: Participant…