ESTRO 2025 - Abstract Book

S4061

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

volumetric modulated arc therapy (VMAT) and 3D conformal radiation therapy (3DCRT). Image-derived (VMAT using CBCT; 3DCRT using 2D kV-MV pair) and SGRT-derived (IDENTIFY TM system) setup shifts were collected on Day 1 of treatment. All patients were positioned using tattoos to derive the corresponding setup shifts, whilst SGRT-derived shifts were recorded immediately before the acquisition of images. For VMAT cases, 6D shifts were derived using cone-beam computed tomography (CBCT) while 3D shifts were acquired with an orthogonal KV-MV pair for 3DCRT cases. A total of 270 positioning shifts were analysed using a two-tailed paired t-test on SPSS (v21.0).

Results:

Table 1 compares the setup shifts derived using SGRT and 2D kV-MV orthogonal pair/ CBCT imaging for the 3DCRT and VMAT cases respectively. In all scenarios, translational shifts were <0.3cm and rotational shifts <1 °. Statistically significant differences were observed in the vertical and rotational shifts for the VMAT cases ( p<0.05 ). Whereas in 3DCRT, the vertical and lateral shifts yielded statistical significance. In general, smaller translational shifts were observed in the VMAT cases compared to 3DCRT cases due to the application of rotational offsets. In VMAT, SGRT- and image-derived shifts exhibited a smaller difference, with significant differences observed only in vertical and rotation directions. Conclusion: The accuracy of SGRT- and image-derived patient positioning in breast radiotherapy are comparable. SGRT can complement traditional image guidance to achieve treatment accuracy (2, 3), reducing imaging doses by minimising the need for repeated imaging. The findings from this study demonstrated the reliability of SGRT for daily setup positioning especially when 6D corrections are applied. Furthermore, the difference in the SGRT- and imaging derived shifts is well within the breast imaging protocol tolerance of 0.5cm. References: 1. Freislederer P, Kügele M, Öllers M, Swinnen A, Sauer T-O, Bert C, et al. Recent advances in surface guided radiation therapy. Radiation Oncology. 2020;15:1-11. 2. Wikström K, Nilsson K, Isacsson U, Ahnesjö A. A comparison of patient position displacements from body surface laser scanning and cone beam CT bone registrations for radiotherapy of pelvic targets. Acta Oncologica. 2014;53(2):268-77. 3. Darreon J, Massabeau C, Geffroy C, Maroun P, Simon L. Surface-guided radiotherapy overview: technical aspects and clinical applications. Cancer/Radiothérapie. 2023. Keywords: SGRT, Setup reproducibility