Dosimetric impact of esophageal motion in esophagus-sparing radiotherapy of spinal metastases
DOI:
https://doi.org/10.2340/1651-226X.2025.44033Keywords:
esophagus, bone metastases, Spine, palliation, Organ at riskAbstract
Background and purpose: The phase III trial (NCT05109819) investigates whether esophagus-sparing radiotherapy (RT) reduces dysphagia in patients with spinal metastases. This retrospective simulation study evaluates the dosimetric impact of inter-fractional esophageal motion in this setting.
Patient/materials and methods: Patients receiving daily image-guided RT on high-quality cone beam computed tomography (CBCT)-equipped units between September 2023 and December 2024 were screened. Inclusion required five consecutive CBCTs with vertebrae T1–T10 in view and a visible esophagus. The esophagus was contoured on the planning CT (pCT) and five CBCTs. Standard and esophagus-sparing 25 Gy/5 fraction volumetric-modulated arc therapy plans were simulated for five thoracic targets. In esophagus-sparing plans, the esophageal D0.027cc was limited to 8 Gy equivalent dose in 2 Gy fractions (α/β = 3 Gy), consistent with the ESO-SPARE constraint. CBCT-based esophagus contours were rigidly transferred to the pCT after bony matching. Esophageal metrics (Mean, D0.027cc–D5cc, V8.5 Gy) were extracted from the original plan and compared across CBCT and pCT contours and between plan types. Inter-fraction motion was assessed using 95% Hausdorff Distance (HD). CBCT quality was evaluated in two patients (five targets) using Dice similarity coefficients and interobserver 95% HDs.
Results: Twelve patients with 23 targets were simulated. Inter-fraction motion led to dose constraint violations in 20 of 23 plans, though only small esophageal volumes entered the high-dose region. Dice scores > 0.8 confirmed good esophageal visibility on CBCT. Most 95% HDs fell within interobserver variability, indicating motion was comparable to contouring uncertainty.
Interpretation: Despite constraint violations, high-dose exposure was limited to small esophageal volumes, and overall sparing was preserved.
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Copyright (c) 2025 Anna Mann Nielsen, Laura Ann Rechner, Sebastian Moretto Krog, Vanja Gram, Morten Hiul Suppli, Patrik Sibolt, Ivan Richter Vogelius, Claus P. Behrens, Gitte Fredberg Persson
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