Effects of head and neck positioning errors and external contour changes on radiation dose in radiotherapy for nasopharyngeal carcinoma
HUANG Anliu
JIA Haibing
HUANG Hui
LIU Shunhua
Abstract：Objective To explore the spatiotemporal evolution laws of head and neck positioning errors and external contour changes in intensity-modulated radiotherapy for nasopharyngeal carcinoma and their cumulative impact on target and organ-at-risk(OAR)dose distribution,and to validate the clinical value of systematic error monitoring and adaptive dose compensation system.Methods A total of 42 patients with newly diagnosed poorly-differentiated squamous cell carcinoma of the nasopharynx admitted to The People's Hospital of Hechi from January 2022 to January 2024 were randomly divided into control group(conventional intensity-modulated radiotherapy,n=21)and observation group(error monitoring+dose compensation,n=21).The control group underwent weekly CBCT,while the observation group used carbon fiber frames,three-plane contour monitoring,and high-frequency CBCT(every 3 sessions)for dynamic error tracking,combined with non-rigid registration and Monte Carlo simulation for dose correction.Observation indicators included positioning errors(X,Y,and Z axes),rates of external contour changes(A,B,and C planes),target doses(GTV D98,CTV1 D95,and CTV2 D95),and OAR doses(brainstem/spinal cord Dmax,parotid gland Dmean,and lens Dmax).Mixed-effects models were used to analyze the correlation between error and dose offset.Results The positioning error in the abdominal and dorsal directions(Z-axis)increased significantly with the number of treatment weeks(r=0.837 9),reaching(1.88±1.15)mm by week 6.When the rate of external contour changes was greater than 7.5%,the error in the head-to-foot direction increased by 36.3%(P=0.029).The observation group improved CTV1 D95 compliance rate by 28.6%,reduced brainstem Dmax exceedance rate to 4.8%,and achieved a Gamma pass rate of 96.8%(91.3%in the control group)through adaptive compensation.Conclusion Positioning errors and external contour changes exhibit spatiotemporal heterogeneity.Systematic monitoring and dynamic dose compensation can significantly improve radiotherapy precision,advocating for clinical adoption of high-frequency CBCT and multimodal registration.
Keywords：nasopharyngeal carcinomaintensity-modulated radiotherapypositioning errorexternal contour changeadaptive radiotherapy
Publication Date：2025-12-28
Online Publishing Date：2026-01-24(First online date of this platform, not the publication date of the document)
Pages：4( 58-61 )