KEY POINTS
- Thermoluminescent dosimeters were placed in an anthropomorphic phantom to measure organ doses from all preconfigured HyperSight protocols on an Ethos 2.1 linear accelerator, covering head, head and neck, thorax, breast and pelvis imaging.
- Effective dose from standard protocols was approximately 0.1 mSv for head, 1.1 mSv for head and neck, 1.4 mSv for thorax, 0.2 mSv for breast, 3.1 mSv for pelvis and 3.9 mSv for pelvis including lymphatics.
- Low Dose protocols reduced absorbed dose by approximately 55% compared with the corresponding standard protocols (p < 0.001). Slow and Large protocols increased dose by approximately 40% and 60%, respectively.
- Anatomically optimized breast protocols reduced dose to the breasts and lungs by up to 80% compared with thorax protocols. The very-low-dose Image Gently protocols often produced warnings for insufficient projection data outside head imaging.
- The system’s partial acquisition trajectory produced substantial asymmetry: beam-facing halves of bilateral organs received, on average, 2.3 times the dose of beam-averted halves. The ratio reached 2.7 in ventral lung measurements.
- For the Thorax Slow protocol, estimated secondary breast-cancer risk on the beam-facing side was 3.7 times that on the opposite side. These estimates were model-based and intended to show relative trends rather than predict individual clinical risk.
- Detailed Results and Discussion report a mean HyperSight head dose of 1.2 mGy versus 2.0 mGy with Halcyon 3.0 and mean bladder and rectal doses of 10 versus 27 mGy with an older On-Board Imager. The abstract appears to reverse the head-dose comparison, an internal inconsistency in the pre-proof manuscript.
CLINICAL TAKEAWAY
HyperSight imaging dose is low relative to therapeutic exposure, but it is not negligible during daily adaptive treatment. Centres should commission indication-specific protocols rather than defaulting to high-dose acquisitions, while accounting for partial-rotation asymmetry; the reported secondary-cancer calculations are illustrative because they depend on phantom geometry, fixed ages and simplified organ-dose assumptions.