Background: Disruptions in cancer care adversely affect patient clinical outcomes, particularly when a patient does not complete the prescribed course of treatment. Adverse outcomes include decreased overall survival and earlier/increased disease relapse or progression requiring additional salvage, palliative, and/or supportive therapies. We have reported on the incidence of treatment terminations (TT) in a large multi-center academic radiation medicine department. This study addresses the healthcare expenditure toward sub-optimal treatment associated with TT. Methods: TT of patients undergoing radiation treatment between 1/2013 and 1/2023 were prospectively tracked as part of departmental quality and safety monitoring. A TT was defined as the discontinuation of therapy at any point following informed consent and treatment simulation. The rate of TT was calculated as a percentage of all new patients who start radiation treatments. Cost of care was estimated using mean values from the 2023 Medicare Part B Fee schedule for New York, accounting for consultation, simulation and planning, treatment delivery, and weekly physician and physics treatment checks prior to TT. Cuts to the Medicare Physician Fee Schedule, Medicare reimbursement, and stagnant Medicare Conversion Factor relative to inflation over the 10 years were not accounted for. Results: There were a total of 1,467 TTs out of 28,707 planned treatment courses (5.1%). The average expenditure prior to TT was $8,584 per patient. Aggregated over the past decade, $12.59 million represents an underestimate of healthcare spend toward these situations at one institution. The rate of TT decreased from 9.3% in 2013 to 3.3% in 2022. As discussed separately, this TT rate was reduced via prospective analysis as part of our ongoing department quality and safety program, with incremental changes to pre-treatment evaluation, on-treatment management, and scheduling processes. Assuming stagnant clinical volume, this translates into decreased spend of $1.48 million annually toward incomplete (sub-optimal) treatments. Conclusions: Radiation TTs reflect major deviations from the original care plan. By understanding reasons for TT, we have more effectively selected optimal treatment paradigms and supported patients proactively through their treatment course. Avoiding divergence from intended cancer care decreases adverse outcomes, thereby improving value of the treatment course.