Evaluation of attenuation-based simulated X-ray images for image-guided radiotherapy
Abstract
In image-guided radiation therapy (IGRT), in-room X-rays are often used for patient positioning and monitoring, however, usually default imaging settings are utilized for each indication. Obtaining patient-specific imaging settings before treatment is achievable using simulated X-rays, which can facilitate IGRT workflow optimization. This study evaluated the image quality of simulated X-rays for thoracic, cranial and pelvic regions. Simulated X-rays were created from computed tomography (CT) scans with indication-specific default settings using a pre-release pilot software, which mimics the geometry of the room-mounted ExacTrac Dynamic (ETD) system (Brainlab SE, Germany). The basis of this algorithm was the Beer-Lambert law. Linear attenuation coefficients were approximated from the CT hounsfield units, while incident intensities were defined by flood images. CT scans were included from three anthropomorphic phantoms and 57 patients (13 lung, 20 glioblastoma, 24 prostate). For evaluation, real X-rays were used as ground truth. Three image quality metrics - Structural Similarity Index (SSIM), Normalized Cross Correlation (NCC), Normalized Mean Absolute Error (NMAE) - complemented by histogram and intensity profile comparisons were used for evaluation. SSIMs for phantom and patient average were 0.87 and 0.80 for the thoracic, 0.94 and 0.88 for the cranial and 0.85 and 0.79 for the pelvic region. Corresponding NCCs yielded values of 0.99 and 0.89, 0.99 and 0.99 and 0.99 and 0.60. NMAEs were 4.1% and 10.7% (lung), 2.6% and 3.2% (brain) and 2.6% and 4.0% (pelvis). Histograms of real X-rays and simulated X-rays (sX-rays) were slightly shifted and showed differences at the background pixel value. Intensity profiles exhibited similar trends with some differences in absolute values. The investigated simulated X-rays demonstrated promising quality for individualized IGRT treatment preparation.
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BibTeX
@misc{jungreuthmayer2026evaluation,
title = {{Evaluation of attenuation-based simulated X-ray images for image-guided radiotherapy}},
author = {Hannah Jungreuthmayer and Julius Arnold and Andreas Renner and Wolfgang Lechner and Maximilian Schmid and Richard Wohlgemuth and Kajetan Berlinger and Dietmar Georg and Barbara Knäusl},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39647},
eprint = {2610.39647},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39647},
}
RIS
TY - UNPB
TI - Evaluation of attenuation-based simulated X-ray images for image-guided radiotherapy
AU - Hannah Jungreuthmayer
AU - Julius Arnold
AU - Andreas Renner
AU - Wolfgang Lechner
AU - Maximilian Schmid
AU - Richard Wohlgemuth
AU - Kajetan Berlinger
AU - Dietmar Georg
AU - Barbara Knäusl
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39647
UR - https://arxiv.org/abs/2610.39647
AB - In image-guided radiation therapy (IGRT), in-room X-rays are often used for patient positioning and monitoring, however, usually default imaging settings are utilized for each indication. Obtaining patient-specific imaging settings before treatment is achievable using simulated X-rays, which can facilitate IGRT workflow optimization. This study evaluated the image quality of simulated X-rays for thoracic, cranial and pelvic regions. Simulated X-rays were created from computed tomography (CT) scans with indication-specific default settings using a pre-release pilot software, which mimics the geometry of the room-mounted ExacTrac Dynamic (ETD) system (Brainlab SE, Germany). The basis of this algorithm was the Beer-Lambert law. Linear attenuation coefficients were approximated from the CT hounsfield units, while incident intensities were defined by flood images. CT scans were included from three anthropomorphic phantoms and 57 patients (13 lung, 20 glioblastoma, 24 prostate). For evaluation, real X-rays were used as ground truth. Three image quality metrics - Structural Similarity Index (SSIM), Normalized Cross Correlation (NCC), Normalized Mean Absolute Error (NMAE) - complemented by histogram and intensity profile comparisons were used for evaluation. SSIMs for phantom and patient average were 0.87 and 0.80 for the thoracic, 0.94 and 0.88 for the cranial and 0.85 and 0.79 for the pelvic region. Corresponding NCCs yielded values of 0.99 and 0.89, 0.99 and 0.99 and 0.99 and 0.60. NMAEs were 4.1% and 10.7% (lung), 2.6% and 3.2% (brain) and 2.6% and 4.0% (pelvis). Histograms of real X-rays and simulated X-rays (sX-rays) were slightly shifted and showed differences at the background pixel value. Intensity profiles exhibited similar trends with some differences in absolute values. The investigated simulated X-rays demonstrated promising quality for individualized IGRT treatment preparation.
ER -