Pulsed Low Dose Rate Radiation Therapy for Gastric Cancer Patients With Peritoneal Metastasis

Inclusion Criteria: * Patients must have histologically-confirmed gastric adenocarcinoma * Patients must have metastasis tumor located within peritoneal cavity * Tumor within the irradiated field is negatively impacting patient's quality of life or threatening catastrophic complication if left untreated as determined by the treating physician * Patient is not a surgical candidate or tumor is not surgically resectable, as documented by surgical oncologist * Patient is not a candidate for, or has not demonstrated a significant local response to chemotherapy, biologic, or other therapies * Patients must have measurable disease per Response Evaluation Criteria in Solid Tumor (RECIST) 1.1 in the irradiated field * Women of childbearing potential must be non-pregnant (negative pregnancy test within 72 hours prior to radiation simulation, postmenopausal woman must have been amenorrheic for at least 12 months to be considered of non-childbearing potential) and nonlactating, and men and women must be willing to exercise an effective form of birth control (abstinence/contraception) while on study and for 3 months after therapy completed * Eastern Cooperative Oncology Group (ECOG) performance status determined to be between 0 and 3 * Absolute neutrophil count (ANC) \>=1,000/ul * Platelets (PLT) \>=75,000/ul * Subjects must sign a written informed consent and Health Insurance Probability and Accountability Act (HIPAA) consent prior to performance of study-specific procedures of assessments and must be willing to comply with treatment and follow-up Exclusion Criteria: * Patients who have had chemotherapy or radiotherapy to the reirradiation target within 4 weeks prior to entering the study * A history of ataxia telangiectasia or other documented history of radiation hypersensitivity * Scleroderma or active connective tissue disease * Active inflammatory bowel disease * Serious, active infections requiring treatment with intravenous (IV) antibiotics * Uncontrolled intercurrent illness including, but not limited to, or psychiatric illness/social situations that would limit compliance with study requirements