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