S2869
RTT - RTT education, training, and advanced practice
ESTRO 2026
Material/Methods: All breast cancer patients who underwent
consistency in clinical image matching practice. As this project was conducted over a two-week period, date collection will be continued to strengthen the representativeness of the study.Figure 1. Radiation Therapists’ confidence levels in matching.
radiotherapy following breast-conserving surgery at our institution between August 2024 and January 2025 were retrospectively included. Patients were immobilized using an all-in-one board. Two regions of interest (ROIs) were defined in the surface-guided radiotherapy (SGRT) system: ROI-B, encompassing the breast target and chest wall up to the mid-coronal plane, and ROI-O, including only the chest wall and adjacent breast tissue.An alternating “SG–CM” positioning protocol was applied, with odd-numbered fractions aligned using SGRT system (ROI-B) and even- numbered fractions aligned using conventional marker-based setup. After each positioning, without altering the patient’s setup, SG was reactivated to record surface registration errors for both ROIs. Six- dimensional setup errors obtained from the two positioning methods and from both ROIs were compared across different planning target volume (PTV) groups.
Figure 2. Uncertainty during image matching reasons.
Keywords: training, treatment, planning
Results: Significant differences (p < 0.05) were observed between SG and CM positioning in the longitudinal (Y: 0.19 ± 1.87 cm vs. 2.26 ± 2.35 cm), vertical (Z: 0.74 ± 1.45 cm vs. 2.31 ± 2.12 cm), and pitch (Ry: 0.88 ± 0.90° vs. 0.93 ± 0.92°) directions.In the small PTV volume group (< 698.05 cm ³ , n = 18), no statistically significant differences (p > 0.05) were found between ROI-B and ROI-O in any translational or rotational direction. In contrast, for the large PTV volume group (> 698.05 cm ³ , n = 18), significant differences were observed in the longitudinal (Y: 2.40 ± 0.98 cm vs. 2.00 ± 0.80 cm) and pitch (Ry: 2.28 ± 1.11° vs. 1.75 ± 0.83°) directions, with ROI-O showing smaller deviations from CBCT compared to ROI-B.
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Investigating the accuracy for SGRT and ROI selection effect on Planning Target Volume variability in intact breast cancer radiotherapy Fengyu Lu 1 , Jiangtao Han 2 , Tantan Li 1 1 Department of Radiation Oncology, National Cancer Center / National Clinical Research Center for Cancer / Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. 2 Department of Radiation Oncology, National Cancer Center / National Clinical Research Center for Cancer / Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Langfang, China Purpose/Objective: To evaluate the overall consistency between surface- guided (SG) and conventional marker-based (CM) positioning in breast-conserving radiotherapy patients, and to compare the positioning accuracy of different regions of interest (ROI) using SG across varying planning target volume (PTV) sizes, with the aim of developing a customized positioning protocol for clinical implementation.
Conclusion: SG positioning significantly reduced setup errors in the lateral, longitudinal, and pitch directions in patients receiving radiotherapy after breast-conserving surgery. The choice of ROI had minimal effect on
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