ESTRO 2024 - Abstract Book

S4101

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Conclusion:

This study shows that when the identification of implanted fiducial markers was limited to a discrete slice of the MR images in MRI-only workflow, uncertainties were introduced. For individual patients the deviation between clinical and observer marker position extended beyond one slice thickness of 2.5 mm and was most prominent in the SI direction. Since these markers are often the sole reference of the prostate position during radiotherapy, this will propagate through the radiotherapy workflow as a systematic uncertainty and impact the positioning of the prostate. The worst-case deviation seen in this study is in the same order of magnitude as CT to MR registration uncertainties, commonly used as an argument for MRI-only prostate radiotherapy. The result of this study motivates the implementation of a marker identification method that is not limited to discrete slices of the MR-volume. Clinically, we will need to address these uncertainties to fully benefit from the potential precision advantage of the MRI-only workflow over a conventional CT/MR-based-workflow.

Keywords: MRI-only, fiducial marker, prostate

2661

Digital Poster

CBCT-based calculation of the dose to target for all fractions in prostate cancer radiotherapy

Rasmus Havelund 1 , Martin Berg 1,2 , Rune S Thing 1,2