ESTRO 2024 - Abstract Book

S3863

Physics - Image acquisition and processing

ESTRO 2024

Chen-Yu Huang, Shang Peng Felix Yung, Ka Ki Lau, Pak Hang Nam, Wai Wang Lam, Hui Geng, Kin Yin Cheung, Siu Ki Yu, Bin Yang

Hong Kong Sanatorium and Hospital, Medical Physics Department, Hong Kong, China

Purpose/Objective:

This study aims to evaluate the image quality of ClearRT helical fan-beam kVCT after the Radixact treatment delivery console (TDC) upgrade in June 2023. Various kVCT image quality metrics were quantified, image artifacts were inspected, and their subsequent dosimetric impact on adaptive radiotherapy was evaluated for both phantom and patient.

Material/Methods:

The kVCT image performance of the head, thorax and pelvis imaging protocols were assessed comprehensively for noise, uniformity, spatial resolution, low contrast visibility, signal-to-noise ratio and contrast-to-noise ratio. A patient with nasopharyngeal carcinoma underwent treatment during the TDC upgrade, with daily kVCT imaging for position verification. A total of nine pre-upgrade kVCT scans and 21 post-upgrade kVCT were collected and evaluated. The beam hardening and discontinuity dark band artifacts that occurred at the air-tissue interface were compared. Additionally, the consequent dosimetric impact on adaptive radiotherapy was evaluated in phantom and patient by re-calculating the same treatment plan on both representative pre-upgrade and post-upgrade kVCT scans associated with respective HU-to-mass density lookup tables.

Results:

Phantom measurements revealed reduced artifacts and improved image quality metrics such as spatial resolution, low-contrast visibility, signal-to-noise ratio and contrast-to-noise ratio. Notably, the noise (standard deviation of water) was reduced by 13, 10 and 15 HU for the head, thorax and pelvis scanning protocols, respectively. Daily patient treatment position verification benefited from fewer beam hardening and discontinuity artifacts, resulting in enhanced soft tissue visibility and CT number fidelity. Reduced imaging artifacts also led to an improvement in the kVCT-based adaptive radiotherapy dose calculation accuracy. Dose calculation on the cheese phantom revealed that compared to the original plan, the deviation of target Dmean decreased from +1.60% for the pre-upgrade kVCT scan, to +0.15% for the post-upgrade kVCT image. Similarly, the dose calculation on the patient’s post-upgrade kVCT images showed a 0.98% improvement of target Dmean compared to the pre-upgrade kVCT.

Table 1. Image quality metrics of the kVCT after TDC upgrade. The value with blue color means the value is better than before, while the value with brown color means the value is worse than before upgrade.