Impact of daily volumetric imaging on target tracking without fiducial markers during robotic treatment of pancreas.
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Embargo End Date
ICR Authors
Authors
Bedford, JL
Nill, S
Oelfke, U
Nill, S
Oelfke, U
Document Type
Journal Article
Date
2026-05-08
Date Accepted
2026-04-20
Abstract
Objective.Treatment of pancreas using Cyberknife is usually accomplished using radio-opaque fiducial markers that can be visualised on the orthogonal kilovoltage imaging system, but implantation of markers can lead to complications. This study therefore describes a method for pancreas tracking without fiducial markers and estimates the improvement in accuracy that can be achieved by additional daily pre-treatment volumetric imaging.Approach.Fiducial markers were artificially removed from the digitally reconstructed radiographs and treatment images of eight previously treated patients. Pancreas position was identified using a combination of local rigid registrations and inter- and intra-fraction motion models. The optimum effect of daily volumetric imaging was simulated by correcting the mean tracking position to match the mean position observed using fiducials. The impact of residual error on the dose distribution was estimated by shifting and recalculating the treatment plan.Main results.Median absolute tracking accuracy without fiducials over the 2823 acquired images is 3.8 mm (range 0.2-19.9 mm) without daily volumetric imaging. The lower bound of accuracy is 2.3 mm (0.1 mm-18.5 mm) when daily volumetric imaging is used. The former scenario reduces theD95%of the planning target volume by a median of 2.5 Gy (1.0-10.2 Gy) compared to the planned dose distribution, whereas the latter scenario reducesD95%by 1.4 Gy (0.4-2.8 Gy). In neither case is theD95%of the clinical target volume (CTV) substantially lowered below the prescription. MedianD0.5ccto critical structures changes by less than 2 Gy.Significance.When tracking the target without fiducial markers, a planning target margin of 3-5 mm is sufficient to ensure that the CTV receives the desired prescribed dose, but the spatial accuracy and target coverage are considerably improved by using daily volumetric imaging.
Citation
Physics in Medicine and Biology, 2026,
Source Title
Physics in Medicine and Biology
Publisher
IOP Publishing
ISSN
0031-9155
eISSN
1361-6560
Collections
Research Team
Radiother Phys Modelling