ESTRO 2025 - Abstract Book

S3639

Physics - Quality assurance and auditing

ESTRO 2025

The Spearman correlations between RMSEs and EPID passing rates (Table 1) are mostly negative, suggesting (correctly) that larger RMSEs lead to lower passing rates. For isocentre 4, which had consistently poor passing rates due to significant patient weight loss in that region, this correlation does not hold.

Conclusion: The EPID offers a possibility to verify patient treatments for multi-isocentric CSI, showing a reasonable correlation between RMSE and passing rate (but not a significant one). For regions suffering from significant weight loss, such as isocentre 4, there is no such correlation. Further data is required to validate the technique.

Keywords: EPID, CSI, monitoring

2493

Digital Poster Evaluation of the Star Shot test for the adjustment and verification of the radiation source position Timo Paasonen Paasonen 1 , Antti Kulmala 2 , Patrik Ikäheimo 1 , Kalle Mikkola 1 1 Cancer Center, Helsinki University Hospital, Helsinki, Finland. 2 Clinical Research Institute HUCH Ltd., Helsinki University Hospital, Helsinki, Finland

Purpose/Objective: To evaluate the suitability of the Star Shot test for quantifying offsets in the radiation source position.

Material/Methods: In a linear accelerator, photon radiation is produced by colliding accelerated electrons with the target. Due to collimator design, if the collision position is not ideal, the radiotherapy beam exiting the device can become eccentric.