PurposeThe Radiation Oncology Case Rate (ROCR) aims to shift radiation reimbursement from fee-for-service (FFS) to bundled payments, which would decouple fractionation from reimbursement in the United States. This study compares historical reimbursement rates from three large centers and a national Medicare sample with proposed base rates from ROCR. It also tests the impact of methodological inclusion of treatment and disease characteristics to determine if any variables are associated with greater rate differences that may lead to inequitable reimbursement. MethodsUsing XXXX electronic medical record data from 2017-2020 and Part B claims from the Medicare 5% research identifiable files (RIF), episodic 90-day historical reimbursement rates for 15 cancer types were calculated per the ROCR payment methodology. XXXX reimbursement rates were stratified by disease and treatment characteristics and multiple linear regression was performed to assess the association of these variables on historical episode reimbursement rates. ResultsFrom XXXX, 3,498 patient episodes were included and 480,526 from the RIF. From both datasets, 25% of brain metastases and 13% of bone metastases episodes included ≥2 treatment courses with an average of 51 days between courses. Accounting for all 15 cancer types, ROCR base rates resulted in an average -2.4% and -2.9% reduction in rates for XXXX and the RIF respectively compared to historical reimbursement. On multivariate analysis of XXXX data, treatment intent (curative vs. palliative) was associated with higher historical reimbursement (+$477 to +$7,417; p ≤ 0.05) for 12 out of 12 applicable cancer types. Stage (3-4 vs. 1-2) was associated with higher historical reimbursement (+$1,169 to +$3,917; p ≤ 0.05) for 8 out of 12 applicable cancer types. ConclusionOur data suggest ROCR base rates introduce an average ≤3% reimbursement rate decrease compared to historical FFS reimbursement per cancer type, which could produce the Medicare savings required for congressional approval of ROCR. Estimating comparisons with future FFS reimbursement would require consideration of additional factors such as the increased utilization of hypofractionation, proposed FFS rate cuts, and inflationary updates. A distinct rate and shortened episode duration (≤ 30 days) should be considered for palliative episodes. Applying a base rate modifier per cancer stage may mitigate disproportionate reductions in reimbursement for facilities with a higher volume of curative advanced stage patients such as freestanding centers in rural settings.