ESTRO 2025 - Abstract Book

S2859

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Material/Methods: This study looked at 3D analysis of different techniques for PTV creation, evaluating displacements using bony anatomy on weekly CBCTs. PCA and dual quaternion methods of spatial displacements were used to construct 6D confidence ellipsoid about the tumor target. The results were compared to a rotational and translational confidence limit (RTCL) method that considered these dimensions as independent and a standard 3mm rolling ball method that provides translational coverage only.

Results:

Image 1 summarizes the percentage of tumor missed and overlap between PTV and PCM in each method. The average percentage of tumor missed in dual quaternion, PCA, RTCL and rolling ball are as followed: 7.6%, 8.8%, 6.3% and 27.03%. The 3mm rolling ball systematically missed in 7/8 cases the same part of the tumor at least twice, which comprised on average 11% of the tumor volume. The dual quaternion, PCA and RTCL methods covered the tumor well, but in 7/8 case the dual quaternion and PCA methods reduced the fraction of the constrictor overlapping with the PTV by between 11% and 45% (average 27%). Conclusion: PTV is needed to ensure target coverage in head and neck radiotherapy. The dual quaternion and PCA method both reduce the overlap between PTV and PCM which can ultimately result in improved patient reported swallowing function, in addition to minimizing the fraction of tumor missed during the course of radiation.

Keywords: spatial displacement, PTV, pharyngeal constrictor

References: 1- Nutting C, Finneran L, Roe J, et al. Dysphagia-optimised intensity-modulated radiotherapy versus standard intensity-modulated radiotherapy in patients with head and neck cancer (DARS): a phase 3, multicentre, randomised, controlled trial. Lancet Oncol. 2023 Aug;24(8):868-880