PROJECT SUMMARY I am a radiation oncologist and early-stage investigator at the Icahn School of Medicine at Mount Sinai. My work has focused on improving the quality of care of older adults undergoing palliative radiation therapy (RT), a treatment used in approximately 500,000 older cancer patients each year to improve quality of life. Palliative RT (PRT) ? RT intended to reduce symptoms rather than achieve cure ? creates both benefits and harms, particularly for older adults in whom cancer occurs in complex settings of multimorbidity and geriatric conditions including functional or cognitive impairments. PRT can dramatically improve symptoms such as pain and neurologic function. Yet it may also cause fatigue, burns, and other adverse effects that can persist for months. Other burdens include weeks of daily travel to attend PRT sessions; painful body positioning due to restricted joint mobility; and tight-fitting face masks which can be terrifying to cognitively impaired persons. If PRT is too burdensome, it is often interrupted or prematurely stopped, limiting its efficacy. Older patients may be particularly vulnerable to PRT as a result of complex and interrelated cancer-specific and geriatric conditions. Yet, little is known about the contribution of these geriatric conditions to PRT-related outcomes, including how they relate to (1) difficulties completing RT; (2) changes in function, hospitalization, and mortality after RT; and (3) self-reported toxicities and quality of life. To address these knowledge gaps, I propose 2 interrelated and complementary studies: (1) a retrospective cohort study of a large, nationally representative sample of adults ?65 years with metastatic cancer from the 2000-2018 Medicare Current Beneficiary Survey (MCBS), which links geriatric assessment data with administrative claims, to (a) determine factors associated with PRT-related outcomes (e.g. completion of RT, function after RT, hospital admission, and mortality) and (b) characterize distinct phenotypic profiles of patient complexity, then examine their associations with the same outcomes; and (2) a prospective cohort study employing more detailed assessments than are in MCBS to (a) further refine associations of PRT with function and QOL and (b) explore associations with self-reported RT- related toxicities. Results from these studies will lead to improved recognition of individuals at high risk of poor PRT outcomes and will support a future R01 application testing a targeted and geriatrics-driven intervention that improves PRT outcomes important to older adults. My long-term goal is to be an independent investigator and leader at the intersection of geriatrics, palliative care, and radiation oncology who improves treatment decisions and designs interventions for older adults receiving PRT. The Beeson Award will support my development in (1) geriatrics and geriatric oncology; (2) population-based observational data and its analyses; (3) prospective study design and implementation in older adults; and (4) leadership in geriatrics to facilitate research dissemination and implementation. These research and training activities will ultimately prepare me to become a leader in aging who aligns RT delivery with the unique needs of older adults with advanced cancer.