title: Analysis of setup error based on CTVision for nasopharyngeal carcinoma during IGRT.
abstract: The aim of the present study was to investigate the role of CTVision in interfractional setup errors during intensity-modulated radiation therapy (IMRT) in 12 nasopharyngeal carcinoma (NPC) patients. The trend of setup errors as a function of time during a fractionated radiotherapy course was investigated, and the influence of reconstructive thickness on image reconstruction for setup errors was analyzed. The appropriate planning target volume (PTV) margin and planning risk volume (PRV) margin were defined to provide a reference for the design of IMRT for NPC. Based on CTVision, online CT was performed weekly for each patient. Setup errors were measured by registration between the CT reconstructed image and reference image. Mean of setup errors, estimated population systematic (Σ), and population random (σ) errors were calculated using SPSS (v15.0). Optimum PTV and PRV margins were calculated. In the clinical data, for the LR (left-right), SI (superior-inferior), and AP (anterior-posterior) directions, Σ was 0.8, 0.8, and 1.0 mm, respectively, and σ was 1.0, 1.3, and 0.8 mm, respectively. In the LR, SI, and AP directions, PTV margins were at least 2.7, 2.9, and 3.0 mm, respectively, and PRV margins were at least 1.5, 1.7, and 1.7 mm, respectively. No significant differences in setup errors were observed during the fractionated radiotherapy course (p > 0.05). However, CT image reconstruction with different thicknesses affected the accuracy of measurements for setup errors, particularly in the SI direction. The application of CTVision to correct setup errors is important and can provide reasonable margins to guarantee the coverage of PTVs and spare organs at risk. A thickness of 3 mm in the reconstructed image is appropriate for the measurement of setup errors by image registration.
authors.affiliation: Affiliated Tumor Hospital of Guangzhou Medical College. gthzsx@163.com.
authors.forename: Shuxu
authors.initials: S
authors.lastname: Zhang
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhou
authors.forename: Quanbin
authors.initials: Q
authors.lastname: Zhang
authors.forename: Shaohui
authors.initials: S
authors.lastname: Jiang
authors.forename: Ruihao
authors.initials: R
authors.lastname: Wang
authors.forename: Guoqian
authors.initials: G
authors.lastname: Zhang
authors.forename: Huaiyu
authors.initials: H
authors.lastname: Lei
authors.forename: Shengqu
authors.initials: S
authors.lastname: Lin
mesh_terms: D000328:Adult; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008207:Lymphatic Metastasis; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000556:secondary; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*