1081 - Incidence and Impact of Incidental Findings in Breast Radiotherapy CT Simulation

Purpose/Objective(s): Computed tomography (CT) simulation is essential in modern breast radiotherapy planning. CT images obtained during simulation may reveal previously unknown incidental findings (IF), which would likely remain undetected without imaging. Institutional practices vary regarding routine radiology review of simulation images, and the impact of this practice on patient outcomes remains unclear. Prior studies have reported low rates of IF; however, these studies were limited by small sample sizes and demographic variability. This study aims to characterize the incidence and nature of IF on CT simulation scans for breast cancer patients, evaluate their impact on patient management, and compare observed rates to those previously reported. This may help determine whether routine radiology review is warranted.

Materials/Methods: A retrospective chart review was conducted of all patients receiving adjuvant breast radiotherapy between December 21, 2022, and January 1, 2025, within a single academic network where all simulation images undergo routine radiology review. Patients were included if they had a CT simulation scan with an official radiology report. Routine demographic and clinicopathologic data were collected. Radiology reports were analyzed to identify presence and nature of IF, and charts were reviewed to determine whether additional tests, treatment, or changes in care resulted. The association between IF and clinical variables was assessed using multivariable logistic regression analysis including age at diagnosis, receptor status, tumor grade, and pathologic prognostic stage as covariates.

Results: 1,268 patients were identified, with IF present in 802 (63.2%) cases. Factors significantly associated with IF included grade (p = 0.05), age at diagnosis (p = 0.03), and pathologic prognostic stage (p = 0.002). Older age was associated with a higher likelihood of IF, whereas higher tumor grade and advanced pathologic prognostic stage were associated with a lower likelihood. Among patients with IF, 290 (36.16%) required additional workup, 50 (6.2%) required additional treatment, and in 21 (2.6%) findings led to major changes in oncology care. According to the Lumbreras classification, 530 (66.1%) findings were minor, 240 (29.9%) were moderate, and 32 (4.0%) were major.

Conclusion: This represents the largest retrospective analysis to date evaluating IF on CT simulation images for adjuvant breast radiotherapy. Our findings suggest a higher incidence of IF than previously reported. While most findings were clinically insignificant, a subset had major implications for patient management. Given the proportion of moderate and major findings, systematic radiology review of simulation images may improve early detection of clinically relevant conditions. Future research will assess the clinical and cost-effectiveness of this practice to determine its impact on patient outcomes.