S2718
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
accuracy1,2. This study compared three compatible masks—DS-Encompass™, M-Encompass™, and Klarity Blue™ SRS Open Face Mask with EasyBite aiming to compare these masks regarding setup reproducibility and alignment accuracy. Material/Methods: A prospective experimental study was conducted and included adult patients ( ≥ 18 years) undergoing brain radiotherapy and treated on the Edge Linear accelerator. Patients were randomized into three groups according to the immobilization mask: Group 1—DS-Encompass™, Group 2—M-Encompass™, and Group 3—Klarity SRS™, and the first three treatment fractions of each patient were considered for the study. CBCT scans were acquired using Head protocol, and the clipbox definition followed departmental anatomical guidelines. Deviations between treatment plan and daily positioning were assessed through:Automatic deviation values obtained from the “Auto-Match” function.Applied deviation values following review by the Radiation Oncologist or Radiation Therapist.Intrafraction motion was monitored using the AlignRT (VisionRT) system, with a 3 mm threshold and a region of interest (ROI) corresponding to the open mask area excluding the eyes. An end of treatment CBCT was performed to verify SGRT’s reliability. Data was analyzed using Excel® Results: Preliminary results include nine patients (3 in Group 1, 4 in Group 2, and 2 in Group 3). Across all groups (Figure 1), mean translational shifts remained below 1 mm, demonstrating high setup reproducibility. However, significant differences were observed in rotational stability. Group 1 showed the highest precision, with minimal variability across all axes and the lowest rotational deviations (RTN = 0.34°, Pitch = 0.29°, Roll = 0.43°) and limited outliers. Group 2 exhibited slightly higher rotational variability (RTN = 0.74°, Pitch = 0.92°, Roll = 0.83°).Group 3 showed the largest deviations, particularly in rotations (RTN = 1.58°, Roll = 1.60°) and wider dispersion.
No treatment fraction showed SGRT detected motion requiring interruption and end-of-fraction CBCTs confirmed all residual shifts were below 3 mm, validating SGRT reliability and accuracy. (Figure.2)
Conclusion: All three systems provided submillimetric translational accuracy compatible with frameless stereotactic treatments, but rotational control varied by design. The dual-shell DS-Encompass™ offered the most stable and reproducible immobilization, supporting its use in high-dose, single-fraction, or multi-target HyperArc applications where rotational precision is critical. References: Ohira S, Haga A, Nihei K, et al. HyperArc VMAT planning for single and multiple brain metastases. Radiat Oncol. 2018;13:159.Komiyama, R., Kokubo, M., Natsume, A., et al. (2021). Intra-fractional patient motion when using the QFix Encompass immobilization system during HyperArc treatment. Journal of Applied Clinical Medical Physics, 22(6) Keywords: HyperArc, Immobilization masks, Reproducibility
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