ESTRO 2025 - Abstract Book

S3186

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Purpose/Objective: The RPS Head (gKTeso GmbH, Germany) is a positioning device, allowing to manually adjust head rotation in three directions (pitch, roll, yaw) prior to radiotherapy treatment. While its use with cone beam computed tomography (CBCT) imaging has been described [1], combining it with surface-guidance technology offers the potential for a faster workflow and reduced imaging dose. This study evaluates the feasibility of rotational corrections using a phantom model, focusing on setup time and precision, and compares surface-guided radiotherapy (SGRT) with conventional image-guided radiotherapy (IGRT) procedures. Material/Methods: The head of an Alderson phantom was immobilized onto the RPS Head platform using a thermoplastic mask. A CT scan served as the reference for both SGRT and IGRT workflows. The phantom head was positioned with defined rotational offsets and subsequently corrected using three approaches: (1) laser-based alignment, (2) SGRT workflow using the LUNA 3D system (LAP Laser, Germany) in combination with the RPS Head platform, or (3) IGRT workflow on an Elekta Synergy LINAC equipped with a Hexapod couch (Figure 1). Positioning was performed by different staff members and setup times were recorded. Post-correction precision was assessed by CBCT imaging.

Results: The SGRT workflow demonstrated shorter setup times compared to IGRT, even though most users had only very limited prior experience with both the RPS Head and the LUNA 3D system (Table 1). The treatment position was more reproducible for both IGRT and SGRT workflows than for setup according to the lasers only (Table 1). However, systematic positional deviations were observed between the different setup techniques, attributed to calibration offsets among the kV imaging system, lasers, and SGRT systems relative to the megavoltage isocentre.