KEY POINTS
- The retrospective analysis included 12 women after breast-conserving surgery—seven right- and five left-sided cases—who had clinically acquired images on both Halcyon 3.1 and Halcyon-HyperSight within ±1 day. All received whole-breast RT 40 Gy/16 fractions plus 10 Gy/4-fraction boost, without regional nodal irradiation.
- HyperSight combines rapid acquisition, an expanded field of view and improved reconstruction/HU calibration. Its breast protocol used an average CTDIvol of 3.39 mGy, compared with 6.04 mGy for Halcyon 3.1 and 7.53 mGy for the reference simulation CT.
- Phantom HU performance was substantially closer to simulation CT. For solid water, mean HU was 6.9±3.1 on simulation CT, 6.4±4.1 on HyperSight and −42.5±47.5 on Halcyon 3.1, illustrating the bias and variability of the older system.
- CBCT-based plan recalculation likewise approached simulation CT more closely. Paddick conformity index was 0.903±0.034 on CT, 0.883±0.053 on HyperSight and 0.840±0.066 on Halcyon 3.1; all pairwise comparisons were statistically significant.
- Relative to simulation CT, HyperSight changed PTV D95 by only −21 cGy, D98 by −51 cGy and V95%Rx by −0.5%. Corresponding Halcyon 3.1 deviations were considerably larger at −157 cGy, −353 cGy and −3.0%, respectively.
- No statistically significant recalculation differences were identified for ipsilateral lung, heart, contralateral breast or maximum dose. Anatomically, a volume present in the original PTV but absent from the adaptive PTV—a potential unnecessary high-dose region if the original plan were maintained—was found in 11/12 patients, averaging 41.2 cm³.
- The analysis remains exploratory: only 12 patients were included, scans were acquired on different days, treatment was free-breathing, and the CBCT-based dose calculation lacked independent verification against repeat CT or measurement. No prospective endpoint demonstrated that HyperSight-guided adaptation improves toxicity or tumor control.
CLINICAL TAKEAWAY
HyperSight appears substantially more suitable than older Halcyon CBCT for quantitative offline breast adaptation, particularly when anatomy changes during a multiweek course. It is promising as a way to identify patients who may need replanning, but this study does not yet define when adaptation should be triggered or prove that repeat CT can routinely be omitted.