ESTRO 2022 - Abstract Book

S545

Abstract book

ESTRO 2022

Image quality of phantom WEPL maps obtained with patient specific FP-PRs was assessed via mean absolute WEPL errors (MAE) and standard deviations (SD), against a reference FP-PR with a complete set of energy layers where no spot-wise energy selection was applied. WEPL accuracy of patient specific FP-PRs was assessed in regions of 4x4 cm2 in the base of skull, neck and brain of the phantom using mean relative WEPL errors (MRE) and SDs with respect to multi-layer ionization chamber PR (MLIC-PR) simulations. Furthermore, a retrospective dataset of in vivo MLIC-PR acquisitions in three head and neck cancer patients was used to further assess WEPL accuracy of patient specific FP-PR simulations (n=10) employing the energy selection algorithm depicted in figure 1. The imaging fields covered 4x4 cm2 and were delivered/simulated around the treatment isocenter from a gantry angle of 90°. MREs and SDs were computed between patient specific FP-PR simulations and in vivo MLIC-PR measurements. Results The image quality analysis showed MAEs ranging from 2.1±5.1 mm (n=26) to 21.0±16.7 mm (n=2) (figure 2(a)). For n<10, MREs up to 11.4±2.8% were found. For n ≥ 10, MREs were below 0.7±1.6% in the three analyzed anatomical regions of the phantom (figure 2(b)). MREs between simulated patient specific FP-PRs (n=10) and in vivo MLIC-PR acquisitions in the three patients were -0.5±1.5%, -0.4±2.8% and -1.9±1.5%.