S2902
RTT- RTT operational practice and workflow innovations
ESTRO 2026
metastases on a Varian TrueBeam STx linear accelerator. All patients were immobilised using the Q- fix Encompass system, with or without a bite block. Each patient underwent two independent setup procedures: manual setup using delta couch shift and SGRT setup using AlignRT, each followed by partial cone-beam CT (CBCT) verification. Six degree of freedom deviations between the planned and CBCT- verified positions were recorded. For each patient, additional data such as sex, age, number of metastases, and use of a bite block were collected. Data were analysed using IBM SPSS 26, applying the Shapiro–Wilk test for normality and the Wilcoxon Signed Ranks Test for paired comparison, with significance set at p ≤ 0.05. Results: AlignRT setup showed significantly smaller deviations in both translational and rotational directions compared to manual setup. Improvements were statistically significant (p < 0.05) for vertical, lateral, yaw, pitch and roll directions, while longitudinal deviations were not significant (p > 0.05). Mean deviations with the AlignRT system were all within submillimeter precision (<1.5 mm and <1° in all axes) compared to manual setup. Use of a bite block further improved lateral stability. No associations were found between setup accuracy and age, sex, or number of Surface-guided setup using AlignRT significantly improves daily positioning accuracy in stereotactic radiosurgery, especially for rotational directions. The system enhances reproducibility, reduces patient- related variability, and provides additional benefit when combined with a bite block. Integrating SGRT into cranial SRS workflows can improve setup metastases. Conclusion: precision, reduce imaging frequency, and optimize treatment efficiency while maintaining submillimeter accuracy. References: Callens D et al. (2024). A prospective randomized study comparing two frameless immobilization systems for cranial stereotactic radiotherapy. Tech Innov Patient Support Radiat OncolSánchez-Rubio P et al. (2024). New findings on clinical experience on surface-guided radiotherapy for frameless non-coplanar stereotactic radiosurgery treatments. J Appl Clin Med PhysZhou S et al. (2022). Initial clinical experience of surface guided stereotactic radiation therapy with open-face mask immobilization for improving setup accuracy: a retrospective study. Radiat OncolDe Ornelas M et al. (2021). Assessment of intra-fraction motion during automated linac-based SRS treatment delivery with an open face mask system. Phys Medica
Conclusion: These findings introduce the first robust dosimetric surrogate metrics for daily heart dose monitoring under limited CBCT FOV conditions, maintaining predictive accuracy even when only 15.5–94.3% of the heart is imaged. The range of heart truncation ensures results are applicable to the FOV capabilities of a wide range of old and new CBCT imaging systems. MHD_lim, in particular, could be integrated into AI- assisted adaptive workflows including synthetic CT frameworks to enable RTT-led decision-making and long-term cardiac risk reduction in breast radiotherapy. Keywords: CBCT, adaptive RT, RTT-led Does the use of Surface-Guided Radiotherapy during Stereotactic Radiosurgery improve the accuracy of patient setup? Klemen Salmi č 1 , Nejc Meki š 2 1 Departmen of Teleradiotherapy, Institute of Oncology, Ljubljana, Slovenia. 2 Department of Medical Imaging and Radiotherapy, University of Ljubljana, Faculty of Health Sciences, Ljubljana, Slovenia Purpose/Objective: This study compared patient setup accuracy in stereotactic radiosurgery using surface-guided radiotherapy (SGRT) and manual setup by assessing translational and rotational deviations to determine whether SGRT improves setup precision. Material/Methods: Digital Poster 667 A prospective study was conducted on 20 adult patients treated with HyperArc SRS for brain
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