{"title":"Does deformation of immobilization devices impact treatment accuracy in thoracic cancer radiotherapy?","authors":"Lianzi Zhao, Louzheng Zhang, Yiwen Hu, Yang Zhong","doi":"10.1002/acm2.14619","DOIUrl":null,"url":null,"abstract":"<p><strong>Background: </strong>Immobilization devices are essential for maintaining accurate and repeatable patient positioning in radiotherapy. This study aimed to evaluate the setup errors and dosimetric deviation induced by the deformation of immobilization devices in thoracic cancer radiotherapy using CT-linac.</p><p><strong>Materials and methods: </strong>A retrospective analysis was conducted on 40 thoracic cancer patients who underwent radiotherapy, using vacuum cushion (VC) and thermoplastic mask (TM) for immobilization. A total of 206 weekly Fan-beam CT (FBCT) images (4-7 per patient) were analyzed to manually delineate immobilization devices and assess their geometric deformations against setup errors. Dosimetric deviations between the clinical plan (CT-plan) and the delivered plan (FBCT-plan) were compared for planning target volume (PTV) and organs at risk (OARs). Correlations between dose variations and setup errors were analyzed in lateral (LAT), longitudinal (LNG), and vertical (VRT) axes.</p><p><strong>Results: </strong>The conformity of the VC (N<sub>up</sub>) and TM (N<sub>down</sub>) with the patient in simulation CT exhibited moderate to strong correlations with VRT setup errors (N<sub>down</sub>: r = -0.484, p < 0.01;N<sub>up</sub>: r = -0.697, p < 0.01). However, intra-fraction deformation of immobilization devices (in FBCT) showed no significant correlation with setup errors. In the dosimetric analysis of OARs, lung dose parameters (D<sub>mean</sub>, V<sub>5</sub>, V<sub>20</sub>) and heart D<sub>mean</sub> exhibited a consistent absolute difference with increasing setup errors. Dose variation decreased significantly when errors exceeded 5 mm, particularly in the VRT direction for most PTV indices, with the exception of CI and HI. Spinal cord D<sub>max</sub> variation correlated significantly with setup accuracy along the LNG axis, but not along other axes.</p><p><strong>Conclusion: </strong>The conformity of immobilization devices in simulation CT exhibits a stronger correlation with setup accuracy than the deformation of these devices in intra-fraction FBCT. FBCT is recommended for improving treatment precision through dosimetric assessment and planning adjustments.</p>","PeriodicalId":14989,"journal":{"name":"Journal of Applied Clinical Medical Physics","volume":" ","pages":"e14619"},"PeriodicalIF":2.0000,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Applied Clinical Medical Physics","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1002/acm2.14619","RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING","Score":null,"Total":0}
引用次数: 0
Abstract
Background: Immobilization devices are essential for maintaining accurate and repeatable patient positioning in radiotherapy. This study aimed to evaluate the setup errors and dosimetric deviation induced by the deformation of immobilization devices in thoracic cancer radiotherapy using CT-linac.
Materials and methods: A retrospective analysis was conducted on 40 thoracic cancer patients who underwent radiotherapy, using vacuum cushion (VC) and thermoplastic mask (TM) for immobilization. A total of 206 weekly Fan-beam CT (FBCT) images (4-7 per patient) were analyzed to manually delineate immobilization devices and assess their geometric deformations against setup errors. Dosimetric deviations between the clinical plan (CT-plan) and the delivered plan (FBCT-plan) were compared for planning target volume (PTV) and organs at risk (OARs). Correlations between dose variations and setup errors were analyzed in lateral (LAT), longitudinal (LNG), and vertical (VRT) axes.
Results: The conformity of the VC (Nup) and TM (Ndown) with the patient in simulation CT exhibited moderate to strong correlations with VRT setup errors (Ndown: r = -0.484, p < 0.01;Nup: r = -0.697, p < 0.01). However, intra-fraction deformation of immobilization devices (in FBCT) showed no significant correlation with setup errors. In the dosimetric analysis of OARs, lung dose parameters (Dmean, V5, V20) and heart Dmean exhibited a consistent absolute difference with increasing setup errors. Dose variation decreased significantly when errors exceeded 5 mm, particularly in the VRT direction for most PTV indices, with the exception of CI and HI. Spinal cord Dmax variation correlated significantly with setup accuracy along the LNG axis, but not along other axes.
Conclusion: The conformity of immobilization devices in simulation CT exhibits a stronger correlation with setup accuracy than the deformation of these devices in intra-fraction FBCT. FBCT is recommended for improving treatment precision through dosimetric assessment and planning adjustments.
背景：在放射治疗中，固定装置对于保持病人准确和可重复的体位是必不可少的。本研究旨在评估CT-linac胸椎肿瘤放疗中固定装置变形引起的安装误差和剂量学偏差。材料与方法：回顾性分析40例胸部肿瘤放疗患者，采用真空垫（VC）和热塑性口罩（TM）进行固定。每周共分析206张扇形束CT （FBCT）图像（每位患者4-7张），以手动划定固定装置并评估其几何变形与安装误差。比较临床计划（CT-plan）和交付计划（FBCT-plan）在计划靶体积（PTV）和危险器官（OARs）方面的剂量学偏差。在横向（LAT）、纵向（LNG）和垂直（VRT）轴上分析剂量变化与设置误差之间的相关性。结果：模拟CT中VC （Nup）和TM （Ndown）与患者的吻合度与VRT设置误差呈中强相关性（Ndown: r = -0.484, p up: r = -0.697, p mean, V5, V20），心脏Dmean随设置误差的增加呈现一致的绝对差异。当误差超过5 mm时，剂量变化显著减小，除CI和HI外，大多数PTV指数在VRT方向上的变化尤为明显。脊髓Dmax变化与LNG轴上的设置精度显著相关，但与其他轴无关。结论：在模拟CT中，固定装置的一致性比在分数内FBCT中固定装置的变形与设置精度的相关性更强。推荐FBCT通过剂量学评估和计划调整来提高治疗精度。
期刊介绍：
Journal of Applied Clinical Medical Physics is an international Open Access publication dedicated to clinical medical physics. JACMP welcomes original contributions dealing with all aspects of medical physics from scientists working in the clinical medical physics around the world. JACMP accepts only online submission.
JACMP will publish:
-Original Contributions: Peer-reviewed, investigations that represent new and significant contributions to the field. Recommended word count: up to 7500.
-Review Articles: Reviews of major areas or sub-areas in the field of clinical medical physics. These articles may be of any length and are peer reviewed.
-Technical Notes: These should be no longer than 3000 words, including key references.
-Letters to the Editor: Comments on papers published in JACMP or on any other matters of interest to clinical medical physics. These should not be more than 1250 (including the literature) and their publication is only based on the decision of the editor, who occasionally asks experts on the merit of the contents.
-Book Reviews: The editorial office solicits Book Reviews.
-Announcements of Forthcoming Meetings: The Editor may provide notice of forthcoming meetings, course offerings, and other events relevant to clinical medical physics.
-Parallel Opposed Editorial: We welcome topics relevant to clinical practice and medical physics profession. The contents can be controversial debate or opposed aspects of an issue. One author argues for the position and the other against. Each side of the debate contains an opening statement up to 800 words, followed by a rebuttal up to 500 words. Readers interested in participating in this series should contact the moderator with a proposed title and a short description of the topic
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