ESTRO 2024 - Abstract Book

S4832

Physics - Quality assurance and auditing

ESTRO 2024

1) Esposito, M., et al. "PD-0578 Quality assurance of EPID transit dosimetry software: results from a multicentric study." Radiotherapy and Oncology 182 (2023): S459-S460.

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Digital Poster

Investigation of image quality of extended kV CBCT acquisitions on Ethos

Szilvia Gazdag-Hegyesi 1,2 , Ádám Gáldi 1,3 , Enikő Koszta 1 , Tibor Major 1,4 , Csilla Pesznyák 1,5

1 National Institute of Oncology, Center of Radiotherapy, Budapest, Hungary. 2 Budapest University of Technology and Economics, Doctoral School of Physical Sciences, Budapest, Hungary. 3 Semmelweis University, Doctoral School of Theoretical and Translational Medicine, Budapest, Hungary. 4 Semmelweis University, Department of Oncology, Budapest, Hungary. 5 Budapest University of Technology and Economics, Institute of Nuclear Techniques, Budapest, Hungary

Purpose/Objective:

Depending on the indication, there are tumours - e.g. central nervous system tumours, pelvic tumours spreading to the para-aortic lymph nodes - that exceed the 24.5 cm field of view of conventional cone-beam CT (CBCT) protocols. In these cases, it is possible to use an extended 38.5 cm field of view for patient position verification. The extended CT acquisitions have an overlapping area of 14 cm longitudinal length, which is scanned at both table positions. The aim of our study is to investigate the consistency of image quality and its applicability in adaptive therapy of these extended CTs over the entire scan length.

Material/Methods:

In particular, the CT number parameters were investigated of the overlapped planes of the images compared to conventional acquisitions, with longitudinal table offsets (from 0 to 15 cm with 5 cm steps in both direction). The measurements were performed for head imaging protocol (100 kV, 138.9 mAs) of the Ethos linear accelerator (Varian) and the reconstruction results with and without iterative CBCT (iCBCT) were compared. The longitudinal consistency of extended CBCT image quality were investigated by Catphan 604 (The Phantom Laboratory) image quality phantom. The analysis of the acquisitions was carried out in the Eclipse treatment planning system (Varian) and using the Smári (The Phantom Laboratory) software.

Results:

Identical CT curves were found when the CT numbers measured at different positions were plotted against the relative electron densities. It is assumed that the best image quality parameters will be found for phantom that is placed in the isocenter of the imaging system. When examining how the CT numbers measured in the isocenter vary as a function of the offsets for conventional reconstruction and iCBCT, smaller differences were detected for the inward longitudinal offset. Compared to the values measured at the isocentre, no substantial differences were found in the