Hypersight Slow-Scan CBCT Supports Reliable Target Delineation and Dosimetric Improvement In Online Lung Adaptive Radiotherapy
Poster
AAPM2026_Lung Adaptive Final.pdf Hosted by AAPM · 0.4 MBAbstract
Purpose
Online adaptive lung radiotherapy has not been widely reported due to challenges in respiratory motion. This study evaluates the clinical performance of HyperSight slow-scan CBCT for target delineation, dose calculation accuracy, and dosimetric benefit in online adaptive lung radiotherapy.
Methods
A retrospective analysis was performed on six patients treated with daily online adaptive hypofractionated or stereotactic lung radiotherapy using the CBCT-based Ethos platform. Two patients received 60 Gy in 8 fractions and four received 50 Gy in 5 fractions. A planning structure was created to boost the ITV center to 120% of the prescription. ITV volumes contoured on slow-scan CBCT were compared with 4DCT maximum intensity projection to assess equivalence in target motion representation. Inter-physician contouring variability was evaluated by comparing primary and covering physician contours. For dose calculation validation, adaptive plans were recalculated on slow-scan CBCT and simulation CT and evaluated using gamma analysis (3%/2 mm, 10% threshold). Dosimetric benefits were assessed by comparing target and organ-at-risk (OAR) dose metrics between adaptive and non-adaptive plans.
Results
The mean ITV volume difference between slow-scan CBCT and 4DCT was 0.7 ± 0.94 cc. Inclusion of covering physician contours increased the difference to 3.3 ± 2.61 cc. Dose comparison resulted in a mean gamma passing rate of 98.9%, with all cases exceeding 97%. Across all patients, adaptive planning was associated with reductions in maximum OAR dose (D0.03cc) relative to non-adaptive plans. Observed reductions included up to 23% for the proximal bronchial tree, 5.8% for the aorta, and 6.2% for the great vessels. For a patient with a target adjacent to the brachial plexus, a 22% reduction was observed. Target coverage increased by 4–8%. Adaptive plans met OAR constraints, whereas corresponding non-adaptive plans failed.
Conclusion
HyperSight slow-scan enables reliable ITV delineation, dose calculation, and dosimetric improvements in online adaptive lung radiotherapy.