Authors: Owen Dillon, Ben Lau, Tess Reynolds, Paul Keall, Vicky Chin, Nabeeha Chowdhury, Shalini Vinod, Jan-Jakob Sonke, Ricky O’Brien
 

ESTRO 2025 Congress Report I Physics track I Imaging and image registration session

Purpose: Four-dimensional cone beam computed tomography (4D-CBCT) is the recommended modality for lung cancer radiation therapy [1]. However, current scan protocols involve long imaging times (240 seconds) and significant imaging doses [2]. Adaptive 4D-CBCT has been developed to enable the application of fast, low-dose 4D-CBCT via standard radiation therapy systems, with the aim of reducing treatment time while improving patient safety and experience [3] while still delivering clinically acceptable images.

Materials and Methods. In the adaptive CT acquisition for personalised thoracic imaging (ADAPT) clinical trial (NCT04070586, ethics approval 2019/ETH09968), adaptive 4D-CBCT was implemented for 30 lung radiation therapy patients. Each patient received conventional 4D-CBCT and adaptive 60-breath and 20-breath scans, in which the scanner adapts the imaging hardware to patient respiration so that data is acquired evenly across the respiratory cycle. The 20-breath scan is reconstructed with the use of a novel motion-compensated algorithm.

The resulting scan images were anonymised, randomised and presented to four radiation therapists and two 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 to verify clinical acceptability of adaptive 4D-CBCT. We quantitatively assessed the image quality in terms of 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 the dose was -55% and -85% respectively, relative to conventional 4D-CBCT. There was no statistically significant difference in the ability of the experts to identify the targets across each pair of scans. This finding indicates that the use of adaptive 4D-CBCT leads to no loss of clinical utility. Across the image quality assessments, there was a statistically significant preference for the 20-breath scan images, probably due to the motion-compensated reconstruction (Figure 1). These trends were repeated in the quantitative assessments of image quality shown in Figure 2; in these assessments, 20-breath scans showed statistically significant improvements in CNR and TIW compared with the 60-breath scans.

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

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

Conclusion: The use of adaptive 4D-CBCT enables the collection of images in 63% less time and with 85% less radiation dose compared with conventional 4D-CBCT, while the images are of the same or better image quality, as assessed by clinical experts.

 

 

Dr Owen Dillon, PhD

University of Sydney, Image X Institute.

Owen.dillon@sydney.edu.au

References:
[1] Iyengar, Puneeth, et al. (2023) "Treatment of oligometastatic non-small cell lung cancer: an ASTRO/ESTRO clinical practice guideline." Practical Radiation Oncology

[2] Thengumpallil, Sheeba, et al. (2016) "Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis." Journal of Applied Clinical Medical Physics

[3] O'Brien, Ricky T., et al. (2021) "The first-in-human implementation of adaptive 4D cone beam CT for lung cancer radiotherapy: 4DCBCT in less time with less dose." Radiotherapy and Oncology

[4] Sweeney, Reinhart A., et al. (2012) "Accuracy and inter-observer variability of 3D versus 4D cone-beam CT based image-guidance in SBRT for lung tumors." Radiation Oncology