ESTRO 2025 - Abstract Book

S3106

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

mask and 282 closed mask treatment sessions. Post-treatment deviations, representing intra fraction movement, was analysed for 92 open mask and 101 closed mask treatment sessions. The observed positional displacement relative to the reference image, both after the initial setup before treatment and following the treatment, are presented in Table 1.

Conclusion: Positioning with the closed mask, guided by markings aligned with laser lines, resulted in less need for correction after kV imaging compared to the open mask and surface scanning system. However, these corrections were generally minor, and the clinical significance of this difference may be negligible. For both mask types, occasional outliers required larger corrections. On average, minimal patient movement was observed during treatment with both masks, and no significant difference was found between them. However, positional changes of up to 4.6 mm were recorded, which could potentially impact clinical outcomes negatively. References: 1. Keane, M., et al., Randomized self-controlled study comparing open-face vs. closed immobilization masks in fractionated cranial radiotherapy. Radiother Oncol, 2024. 196 : p. 110314. 2. Li, G., et al., Migration from full-head mask to "open-face" mask for immobilization of patients with head and neck cancer. J Appl Clin Med Phys, 2013. 14 (5): p. 243-54. 3. Zhao, B., et al., Minimal mask immobilization with optical surface guidance for head and neck radiotherapy. J Appl Clin Med Phys, 2018. 19 (1): p. 17-24. 4. Lundin, E., S. Axelsson, and E. Ohlsson-Nevo, Open or closed: Experience of head and neck radiotherapy masks - A mixed-methods study. J Med Radiat Sci, 2024. Keywords: Mask, Immobilisation