RecruitingPhase 1ProcedureAtezolizumab in Combination With Stereotactic Body Radiation Therapy (SBRT) and Surgery for Relapsed OsteosarcomaThis study aims to determine the safety and tolerability of combined Atezolizumab, stereotactic body radiation therapy (SBRT), and surgical resection of pulmonary metastases in patients with pulmonary recurrence of osteosarcoma