ESTRO 2024 - Abstract Book

S4875

Physics - Quality assurance and auditing

ESTRO 2024

Results:

The mean 3D spatial deviation to the expected position are 0.85±0.06 mm (1 SD) , 0.80±0.07 mm, 0.84±0.08 mm, 0.96±0.06 mm, 1.05±0.08 mm and 1.08±0.08 mm for the ball bearing ISO, 1, 2, 3, 4 and 5 respectively.

Conclusion:

The observed deviations from the expected positions differ slightly with those reported by Pokhrel et al. 2023 [1], but they are still within the DEGRO/DGMP recommendations for some fractionated stereotactic radiotherapy indications (i.e 3D spatial deviation threshold ≤ 1.25 mm, if no radiation-sensitive critical structures are close) [2]. The phantom positioning, the laser and radiation isocenter position as well as the MV-kV panel position alignment can introduce deviations to the spatial accuracy. The WL test can help to evaluate the isocenter alignment and setup accuracy in order to reduce the total uncertainties of the linear accelerator. Since there is an interest for some units to perform stereotactic treatment using the Halcyon linear accelerator [3, 4], a well-established stereotactic QA should be implemented in order to evaluate the spatial accuracy of this machine. Based on the validation and the implemented QA process, internal recommendations should be given to select the patients (tumor location, size, indications) which can be accepted for SRS treatments at Halcyon.

Keywords: Winston-Lutz test, SRS, Halcyon

References:

[1]: Pokhrel D, Mallory R, Bernard ME. The spatial accuracy of ring-mounted halcyon linac versus C-arm TrueBeam linac for single-isocenter/multi-target SBRT treatment. Med Dosim. 2023 Autumn;48(3):170-175. doi: 10.1016/j.meddos.2023.03.005. Epub 2023 Apr 13. PMID: 37059628.