ESTRO 2025 - Abstract Book

S2761

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

ESTRO 2025

The script was evaluated on three clinical SRS plans, each containing 15 or more lesions. The accuracy of detected dose islands, volume, dimensions, and lesions enclosed within each dose island was confirmed. Figure 2 illustrates (a) a 12 Gy dose island surrounding 3 lesions within a 25-lesion SRS plan and (b) an example output reported by the script, demonstrating its comprehensive capability and consistency. Conclusion: We successfully developed a script that isolates individual dose islands, reports geometry information, and identifies which lesions are enclosed. This tool can significantly enhance the evaluation of multi-mets SRS plans by conforming with the HyTEC standards and can support data collection for retrospective analyses and correlation with treatment-induced radiation necrosis.

Keywords: SRS, Dose Islands,Radiation Necrosis

References: [1] Milano MT, Grimm J, Niemierko A, et al. Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain. Int J Radiat Oncol Biol Phys. 2021;110(1):68-86

1353

Digital Poster Feasibility Study on Dosimetric Impact of Carotid Artery Dose Sparing Optimised Volumetric Modulated Arc Therapy (VMAT) for early Glottic Cancers. Becky Lloyd 1 , Lisa Bell 1 , Hannah Richardson 1 , Shanmugasundaram Ramkumar 2 , Ian S Boon 2,3 1 Department of Radiotherapy Physics, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom. 2 Department of Clinical Oncology, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom. 3 Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom Purpose/Objective: Carotid artery dose constraints as an organ at risks (OAR) are not well established and not routinely optimised for in head and neck radiotherapy (1) . Radiation to neck is attributed to cause late toxicities of carotid artery stenosis and ischaemic stroke (1),(2) . Early glottic squamous cell cancer has a high curative rate. Primary aim is to investigate feasibility of carotid artery dose sparing optimisation in VMAT radiotherapy planning and impact on adjacent OARs. Secondary outcome is to investigate the optimal radiotherapy arc placement for early glottic cancers. Material/Methods: This is a retrospective dosimetry feasibility study. 10 early glottic cancers clinically staged T1-2N0M0 treated with curative intent radiotherapy 55Gy in 20 fractions over 4 weeks were included. A single consultant oncologist contoured bilateral carotid arteries, constrictor muscles, parotids and brachial plexus according to international atlas (3) . VMAT radiotherapy was re-planned and optimised for carotid artery sparing and dosimetric impact on adjacent OARs were assessed. Dose comparisons were made between A) Original plan. 1 or 2 partial arcs, no carotid sparing B) Replanned with 1 or 2 partial arcs and carotid sparing (optimised for a mean dose of 25Gy) C) Replanned with 1 full arc and carotid sparing

Results: Dosimetric impact

Dosimetry analyses ( Table 1) showed current VMAT radiotherapy with partial arcs without carotid sparing achieved a mean dose to the right and left carotid artery of 24.5Gy and 21.6 Gy respectively. VMAT optimisation for carotid