ORIGINAL RESEARCH article
Front. Oncol.
Sec. Radiation Oncology
This article is part of the Research TopicPrecision Medical Imaging for Cancer Diagnosis and Treatment Volume IIIView all 8 articles
Comparison of Positioning Errors and PTV Expansion between the iSCOUT Image-Guidance System and Onboard EPID in Rectal Cancer Radiotherapy: A Real-World Study
Provisionally accepted
- Cancer Hospital Chinese Academy of Medical Sciences Department of Radiation Oncology, Beijing, China
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The iSCOUT orthogonal imaging system and onboard EPID system are commonly used for image-guidance positioning in conventional linear accelerators, but studies comparing the two are scarce. This research aims to analyze and compare the differences and consistency between the iSCOUT and onboard EPID systems in rectal cancer patients in the prone position. Patients were grouped based on factors such as rectal tumor location, BMI, age, and gender. Additionally, the study classifies tumor locations within the rectum to evaluate PTV (Planning Target Volume) margin expansion for different rectal locations, providing a reference for determining optimal PTV margins in rectal cancer treatment. A retrospective analysis was conducted on 277 rectal cancer patients positioned prone on a Belly Board. During radiotherapy, at least three position verifications were performed in the first week, followed by weekly verifications. Both iSCOUT and onboard EPID image-guidance systems were used simultaneously for these verifications. Systematic and random errors, as well as the consistency of fixed positioning, were evaluated based on images from both systems taken in the same position. Patients were grouped by tumor location, BMI, age, and gender. The positioning errors and PTV margins for each group were calculated to analyze relevant patterns. Kappa consistency in the left-right (LR) and superior-inferior (SI) directions was better compared to the anterior-posterior(AP) direction (LR = 0.794, SI = 0.852, AP = 0.610). Patients with tumors located in the upper rectal location require larger PTV expansions compared to those with middle or lower tumors. Obese patients with a BMI≥28 exhibited significantly larger PTV expansions than other groups. Age based grouping revealed an inverse relationship between age and PTV margin expansion. No significant differences were observed when grouped by gender.
Keywords: Image guidance5, Positioning Error3, PTV expansion4, Radiotherapy1, Rectal Cancer2
Received: 23 Jul 2025; Accepted: 19 Dec 2025.
Copyright: © 2025 Wan, Hou, Han, Zheng, Liu, Sun, Zhao, Huan, Wang and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Hongkai Wang
Tantan Li
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