If requirements for expansion are met, another 14 patients will be recruited for Stage 2. Inclusion Criteria (summarized) 1. Patient willing and able to provide written informed consent for the trial. 2. Patient age ≥ 18 at time of consent. 3. Unresectable or stage IV malignant pleural or peritoneal mesothelioma (MPM). 4. Histological and/or cytological confirmation of MP M. 5. At least one prior therapy 6. At least one targetable lesion appropriate for palliative SBRT. 7. Karnofsky Performance Score (KPS) ≥ 70% 8. Adequate organ function, defined below in Section 6.1 Memorial Sloan Kettering Cancer Center IRB Number: 17- 358 A(7) Approval date: 25 -Feb-2022 Page 9 of 51 Exclusion Criteria (summarized) 1. Currently participating and receiving another study therapy or has participated in a study of an investigational agent and received s t u d y therapy or used an investigational device within 4 weeks of the first dose of treatment.