S2740
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Purpose/Objective: Open-face masks provide an alternative
setup position using X-ray imaging for each SGRT calibration method is shown in figure 1. The overall maximum shift discrepancies between SGRT and stereoscopic imaging was 1.05 mm in the translational direction and 0.65 degrees in the angular direction prior to cube calibration commissioning. The maximum overall discrepancies between the two systems were reduced to 0.76 mm in the translational direction and 0.59 degrees in the angular direction.
immobilisation method for head and neck (H&N) radiotherapy that may improve patient comfort and reduce claustrophobia. Unlike conventional closed- face masks that cover the entire face, open-face masks offer a less restrictive option. However, improved comfort must be balanced with setup accuracy and precision.This study evaluated the inter- and intrafraction variations of open-face and shoulder (OF) compared with conventional closed-face and shoulder (CF) thermoplastic masks used in radical H&N treatments. Material/Methods: This prospective study recruited 41 patients with H&N cancer who were consented and treated with radical intent between June 2024 and August 2025 at a single institution. All patients were immobilised using personalised Instaform™ foam neck rest and 3.2 mm head, neck, and shoulder white Hexspand™ thermoplastic mask (CDR Systems, Calgary, Canada). An open drape, not covering the face was used for the OF group, whereas a standard closed drape was used for the CF group.All patients were treated on TrueBeam (v2.7, Varian Medical Systems, Palo Alto, USA). The OF group was setup and monitored using AlignRT Advance (v6.3 MR1, Vision RT, London, UK) SGRT system, while the CF group was setup with marks on mask and monitored via closed-circuit television.IGRT was performed using kV/kV imaging with 2D/3D matching for all patients. The initial IGRT matches (in 6DoF) were analysed for interfraction variations. Pre- and post-treatment CBCTs were acquired weekly, and the differences between pre- and post-treatment auto-matches were analysed for intrafraction variations.Variations were compared between groups using a Mann-Whitney U test (p ≤ 0.05). Results: Of the 41 patients, 22 were immobilised with OF mask and 19 with CF mask. Inter- and intrafraction variations were assessed using 1,307 kV/kV image pairs (728 OF, 579 CF), and 259 pre- and post- treatment CBCTs (140 OF, 119 CF).There were statistically significant differences between the groups for interfraction vertical, long, lateral and roll, however the median interfraction variations were all within 0.21 cm and 0.1 degrees for both groups. There were no significant differences between the groups for intrafraction variations and the median variations were all within 0.02 cm and 0 degrees. Inter- and intrafraction variations are summarised in Table 1 and shown in Figure 1.
Figure 1: Plot of vector magnitude deviation for SGRT plate and cube calibration methods for the range of
couch angles. Conclusion:
Overall, this study found that there was a pronounced improvement in SGRT position verification accuracy when compared to stereoscopic x-ray imaging as a baseline, once cube calibration was introduced. These findings support the need to integrate cube calibration into departmental workflow for SGRT-guided, open- faced and non-coplanar radiotherapy. References: 1. Zhang L, Vijayan S, Huang S, Song Y, Li T, Li X, et al. Commissioning of optical surface imaging systems for cranial frameless stereotactic radiosurgery. Journal of Applied Clinical Medical Physics. 2021 Mar 29;22(5):182–90. doi:10.1002/acm2.13240 Keywords: SGRT. Non-coplanar, sterecropic x-rays Inter- and intrafraction variations of patients immobilised with open-face masks for head and neck cancer Kenton Thompson 1,2 , Julianne O’Shea 1 , Karen McGoldrick 1 , Vanessa Panettieri 1,2 , Katrina Woodford 1,2 , Andrew Coleman 1 , Christopher Daniels 1,2 , Duc Tran 1 , Arnulf Mayer 1 , Tsien Fua 1,2 , Sandro Porceddu 1,2 1 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 2 Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia Proffered Paper 3801
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