<h3>Purpose/Objective(s)</h3> The Oncology Care Model (OCM) is an alternative payment model aimed at providing higher quality, lower cost care to participating Medicare beneficiaries. However, information regarding trends in spending, particularly for radiation oncology (RO) services, is limited. <h3>Materials/Methods</h3> We identified 17,157 episodes of care from 9,898 patients treated at a statewide multispecialty health system through the first eight six-month Performance Periods (PP1-8; July 1, 2016 to June 30, 2020) of the OCM. Aggregate spending stratified by 10 expenditure domains (e.g., Part B/D drugs, RO, etc.) and 21 disease sites was extracted from claims data. A subset analysis of RO expenditures was performed on 2,149 episodes from 2,033 patients treated with radiotherapy (RT). All expenses are expressed in per beneficiary, per episode (PBPE) terms indexed to average PBPE. <h3>Results</h3> Indexed to the average PBPE payment, average expenditures increased (P<sub>trend</sub> < 0.001) from 92% in PP1 to a peak of 111% in PP7. Part B and D drugs were used in 87% and 23% of episodes, whereas RO services were used in 13%. Part B spending increased from 41.9% of PBPE expenses in PP1 to 45.6% in PP8 and Part D spending increased from 17.0% to 22.6%, whereas RO spending decreased from 2.6% to 2.4%. Physician services and in-hospital costs also decreased from 11.2% and 11.4% to 8.4% and 8.3%, respectively. By disease site, the largest PBPE expenses were for melanoma (234%), multiple myeloma (226%), and kidney cancer (191%), for which Part B/D spending accounted for 77%, 82%, and 81% of spending for each site, respectively. Among sites with the highest total expenditures, increases in Part B/D spending from PP1-8 were seen for breast (+11%), multiple myeloma (+11%), lung (+12%), and prostate (+7%), and chronic leukemia (+12%). Among sites with the highest RO spending, decreases in RO expenses were seen for breast (-1%), lung (-1%), and female genitourinary (-4%), while an increase was seen for prostate (+4%). On subset analysis, the average number of RT fractions per episode decreased from 19.2 in PP1 to 18.6 in PP8; this decrease was seen for breast (-2.1) and lung (-2.8) cancers but not for prostate (unchanged). Intensity-modulated RT charges accounted for 51% of RT spending and increased 5% from PP1-8, whereas 3D/electron external beam made up 21% and decreased 8%. Expenses for image guidance (17%; +2%), stereotactic RT (9%; +1%), radiopharmaceuticals (1.4%; +0.5%), and brachytherapy (1.4%; +0.5%) all increased. <h3>Conclusion</h3> The total cost of oncology care continues to rise, driven by increases in Part B and Part D drug spending. Conversely, RO expenditures were small and decreased on a relative basis over the study period. Future payment models directed at meaningfully managing the total cost of cancer care will need to prioritize high cost and high growth areas of spending, including novel drug therapies, while accounting for patient outcomes.