Radiotherapy (RT) access in Guatemala is severely limited, with four total clinics and a single public facility for underserved patients. As part of an ongoing collaborative US-government-funded project between this single public facility (overseas institution, OSI) and an academic US organization (USO), a state-of-the-art LINAC was installed at the OSI in 2019. Prior to this, RT at the OSI was limited to non-image-guided, 2D/3D technique, without multi-leaf collimation or routine customization of blocks. We hypothesized that installation of a state-of-the-art LINAC would enable improved clinical outcomes at the only public cancer hospital in Guatemala by advancing the types of RT offered to a diverse and underserved patient cohort. The USO Institutional Review Board approved this study with support of OSI leadership. Records and registry data for the first 35 patients sequentially treated on the new OSI LINAC from November 2019 - February 2020 were compiled by the OSI team, de-identified, then analyzed by the joint OSI and USO group. RT plans were created through an ongoing OSI and USO collaboration. Data collected and analyzed include sociodemographics, clinical features, RT planning metrics, and 6-week CTCAEv5 toxicity outcomes. Among the first 35 patients treated on the modern LINAC, 17% were >65-years-old, and 49% were women. 77% were of non-indigenous background (“ladino” or “mestizo”) and 23% identified as indigenous. Patients traveled a mean distance of 105 km to the OSI clinic. Monthly income ranged from $0 to $327, 23% were uninsured, and 82% did not pay for RT. All patients received RT to the primary tumor, with median of Stage II disease, and common sites including CNS (23%), H&N (17%), and GU (14%). All plans were VMAT with MV-CBCT, and included incorporation of simultaneous (2) and sequential (8) boosts. In the absence of the new LINAC, the alternative RT modality determined by treating physicians would have been 3D in all cases. Median PTV margin was 6mm (range 1-25mm) with mean 100% PTV coverage 99.8 ±2.8% of prescription dose. The median number of organ-at-risk constraints per plan was 3 (range 1-15). One patient with prostate cancer did not complete RT due to CTCAEv5 grade 2 urinary toxicity deemed secondary to a drug-drug interaction, unrelated to RT. Rates of Grade 2 and 3+ toxicity in assessed patients (26/35) at 6 weeks post-RT were both 0%. The installation of a state-of-the-art LINAC at the only cancer center for underserved patients in Guatemala led to advancement in RT techniques for a diverse patient group with a broad range of cancers, in a region with limited RT capacity. Amidst a global RT crisis, our experience indicates that close partnerships between US institutions and low-resource countries can elevate the global standard for RT care.