Hypersight Slow-Scan CBCT Supports Reliable Target Delineation and Dosimetric Improvement In Online Lung Adaptive Radiotherapy
Abstract
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.