Retrospective Analysis of Shape and Dosage Changes in Structures during Radiotherapy for Head and Neck Cancer Patients Based on Velocity 📝

Author: Daming LI, Jinsen Xie, Zhe Zhang 👨‍🔬

Affiliation: Peking University Shenzhen Hospital Radiotherapy Department, School of Nuclear Science and Technology, University of South China 🌍

Abstract:

Purpose: To analyze the actual doses received during radiotherapy for head and neck cancers (HNC) using Velocity, providing insights for adaptive radiotherapy decision-making.
Methods: Thirty-three HNC patients were selected. Weekly CBCT scans and NRS 2022 nutrition assessments were performed. Velocity was used to deformably register CBCT and planning CT (Pct) into synthesized CT (Sct) images, and dose recalculations were done without changing plan parameters. DICE similarity coefficient (DSC), Hausdorff distance (HD), volume changes, external body volume ratio (REBV), Dmin for the target, Dmax for serial organs, and Dmean for parallel organs were calculated. The dose distributions and 3D gamma passing rates (GPR) were compared, and GPR’s correlation with REBV was assessed.
Results: The patients experienced an average weight loss of >10% in 28 days, with NRS 2022 scores reaching 3 (range: 7–43). A total of 232 CBCTs were converted to Sct. Significant deformations occurred in the bilateral parotid glands (PG) and CTVnd. The average DSC, HD, and volume changes for left PG were 0.87, 4.70 mm, and -12.33%, and for right PG, 0.86, 4.71 mm, and -12.95%. Dmin for CTVnd decreased (51.98 vs. 47.68 Gy, p = 0.009), while Dmax for the brainstem increased (45.31 vs. 46.21 Gy, p = 0.001). The Dmean for the right PG increased by 1.3 Gy (p < 0.001), and for the left PG, the Dmean increased by 0.3 Gy (p > 0.05). The GPR at 2%/2mm was 96.41%, with a moderate correlation to REBV (R > 0.8).
Conclusion: Body shrinkage is common in radiotherapy and moderately correlates with GPR. The parotid glands and CTVnd are more affected by shrinkage, but the severity of deformation does not always result in significant dose changes. Further analysis is needed.

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