Radiation Therapy for the Treatment of Metastatic Gastrointestinal Cancers

PRIMARY OBJECTIVE: I. To determine whether radiation therapy can convert overall response rates from progressive disease to stable or responsive disease as measured by Response Evaluation Criteria in Solid Tumors (RECIST) version (v.) 1.1. SECONDARY OBJECTIVES: I. To define overall response rate by immune-Modified Response Evaluation Criteria in Solid Tumors (iRECIST) criteria. II. To determine time to progression. III. To determine overall survival. IV. To determine local control in radiated lesion(s). V. To characterize the effect of distant radiation on unirradiated target lesions. VI. To describe the incidence of new metastatic lesions. VII. To determine treatment safety by Common Terminology Criteria for Adverse Events (CTCAE) v. 5.0. VIII. To describe time to new systemic therapy. EXPLORATORY OBJECTIVES: I. To define radiation-induced effects on circulating immune cells. II. To describe remodeling of the circulating T cell repertoire by deep sequencing of variable, diversity and joining (VDJ) regions of T cell receptors (TCRs). III. To describe changes in circulating tumor deoxyribonucleic acid (DNA) (ctDNA). OUTLINE: Patients undergo radiation therapy for a total of 5 treatments over 5-9 calendar days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 14 day, 6 months, and then up to 36 months.