ExacTrac Dynamic Surface-Guided Setup Versus Tattoo-Based Positioning in Breast Cancer Radiotherapy: A Retrospective...

Background/Objectives: Accurate and reproducible patient positioning is essential in breast cancer radiotherapy to ensure target coverage while minimizing exposure to surrounding healthy tissues. Conventional tattoo-based alignment remains widely used but has inherent limitations, including variability, potential setup errors, and negative psychological impact from permanent markings. Surface Guided Radiation Therapy (SGRT) using ExacTrac Dynamic (ETD) offers a non-invasive, real-time alternative that may improve workflow efficiency and patient experience. This study evaluated the accuracy and efficiency of ETD compared with conventional tattoo-based setup in breast-only radiotherapy. Methods: We conducted a retrospective comparative cohort analysis of patients treated for breast cancer at Shaare Zedek Medical Center between December 2022 and December 2024. Forty-nine patients (245 fractions) were positioned using SGRT with ETD, while a control cohort of 20 patients (100 fractions) underwent conventional tattoo-based alignment; all patients received breast-only irradiation (26 Gy in 5 fractions) in deep inspiration breath-hold (DIBH), and all received daily kilovoltage (kV) imaging, which served as the reference. Six-dimensional pre-correction setup deviations and treatment preparation times were recorded. Because fractions from the same patient are correlated, the primary analysis was performed at the patient level (random-intercept model, equivalent to comparison of patient means in this balanced design), with patient-level (cluster) bootstrap confidence intervals, Bonferroni correction across the six axes, and rank-biserial effect sizes. Results: Setup errors were strongly clustered within patients (intraclass correlation up to 0.75). At the patient level, absolute setup errors did not differ significantly between cohorts on any axis (all p ≥ 0.11), nor did composite translational (p = 0.27) or rotational (p = 0.70) errors. SGRT showed a mean vertical offset of -5.1 mm relative to control (95% CI -8.9 to -1.3 mm; p = 0.013, Bonferroni-adjusted p = 0.078). Clinically significant pre-correction deviations (≥5 mm) occurred in 52-65% of fractions in the vertical and longitudinal directions in both cohorts. Mean preparation-for-treatment time was shorter with SGRT (11.0 vs. 13.9 min; median 10.0 vs. 12.5 min; p = 0.036). Conclusions: Initial setup with ExacTrac Dynamic showed no statistically significant difference in setup accuracy compared with tattoo-based setup and shortened preparation time but was associated with a vertical offset. Pre-correction errors were large with both methods, so daily image guidance remains necessary. Because backup tattoos were placed in all patients and equivalence was not formally tested, these results support-but do not establish-tattoo-free daily setup. Prospective, multicenter studies are warranted to validate these findings and assess long-term clinical outcomes.