ESTRO 2025 - Abstract Book

S3220

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

1065

Digital Poster Goodbye face masks! Accurate and patient-friendly head and neck radiotherapy using individual dorsal masks and surface guidance. Marion Essers, Lennart Mesch, Maaike Beugeling, Eva de Wee, Robert Poorter, Willy de Kruijf Radiation Oncology, Institute Verbeeten, Tilburg, Netherlands Purpose/Objective: Using surface guided radiotherapy (SGRT), head and neck (H&N) cancer patients may undergo radiotherapy without the discomfort and stress of a restricting facemask [1,2]. However, when positioned on a standard head rest, treatment would have to be interrupted in too many fractions (19%) to maintain the clinical target volume to planning target volume (CTV-PTV) margin of 3 mm [1]. An individual dorsal mask might give more support and stability. In this study, the patient setup accuracy, number of necessary treatment interrupts, and intrafraction motion for H&N cancer patients positioned using an individual dorsal mask and monitored using SGRT was examined. Material/Methods: Thirty H&N patients with 15 to 35 treatment fractions were enrolled in this study between January and July 2024. If possible, the patient was positioned using only the posterior shell of the DSPS- Prominent ® mask (Macromedics). SGRT (Identify, Varian Medical Systems) was used for initial setup, and a cone-beam CT (CBCT) was acquired to perform online setup correction. SGRT was also used for intrafraction motion monitoring, and to reposition the patient when an intrafraction motion threshold of 2 mm or 2° (th 2 ) was exceeded. When the patient was repositioned, or at least once a week when no repositioning was needed, a CBCT was acquired after the fraction to determine the intrafraction motion, and the resulting CTV-PTV margin for intrafraction motion. Results: The dorsal mask was not suitable for 3 patients, and one patient eventually did not receive radiotherapy, hence data of 26 patients and a total of 720 treatment fractions were included. For 1.1% of fractions, the patient had to be repositioned because of motion or coughing during/after the CBCT, and for 4.4% of fractions because of inaccurate patient posture. For only 3.5% of fractions, the treatment had to be interrupted for repositioning because the intrafraction motion exceeded th 2 . The intrafraction motion is shown in Figure 1. The CTV-PTV margin for intrafraction motion is 1.1 mm in all directions, even smaller than the margin in lateral direction in the face mask in our feasibility study [1]. A total CTV-PTV margin of 3 mm can be applied.