ESTRO 2025 - Abstract Book

S3013

Physics - Image acquisition and processing

ESTRO 2025

2019/ETH09968) implemented adaptive 4DCBCT for 30 lung radiation therapy patients. Each patient received conventional 4DCBCT and adaptive 60 breath and 20 breath scans, where adaptive scans adapt imaging hardware to patient respiration to acquire data evenly across the respiratory cycle. The 20 breath scan is reconstructed with a novel motion compensated algorithm. The resulting scan images were anonymised, randomised and presented to 4 Radiation Therapists and 2 Radiation Oncologists for qualitative assessment. They were asked to assign task specific ratings [4] of target visibility, and overall image quality on a 10-point scale. The responses were sorted by patient and paired t-tests used to assess preference for scan type and verify clinical acceptability of adaptive 4DCBCT. We performed quantitative assessment of image quality as Structural Similarity (SSIM), Contrast to Noise Ratio (CNR) and Tissue Interface Width (TIW). Results: The 60 breath and 20 breath scan times were +1% and -63% and dose -55% and -85% respectively relative to conventional 4DCBCT. The qualitative expert image assessment found no statistically significant difference between each scan type in the ability of the expert to identify the target indicating that adaptive 4DCBCT maintains clinical utility. In the overall image quality assessments there was a statistically significant preference for the 20 breath scan images, likely due to the motion compensated reconstruction, figure 1. These trends repeat in the quantitative assessments of image quality, figure 2, where 20 breath scans had statistically significant improvements in CNR and TIW.

Figure 1: Example scan images. Note the increased image noise in the 60 breath scan due to halving the imaging dose, and the smoothing of the 20 breath scan due to the motion compensated reconstruction algorithm.

Figure 2: Image quality metrics across all acquired scans. Note SSIM is relative to conventional scan.

Conclusion: Adaptive 4DCBCT enables imaging with 63% less time and 85% less dose while delivering same or better image quality as assessed by clinical experts.

Keywords: 4DCBCT