This phase II trial studies the side effects and response of pulsed low dose rate radiation therapy in treating gastric cancer patients with peritoneal metastasis.

This phase II trial studies the side effects and response of pulsed low dose rate radiation therapy in treating gastric cancer patients with peritoneal metastasis. Radiation therapy uses pulsed low dose rate high energy X rays to kill tumor cells and make less side effects than conventional 3-dimensional conformal radiation therapy. Palliative radiation therapy may help gastric cancer patients with peritoneal metastasis live more comfortably.

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