title: A simple method of evaluating margin-growing accuracy in image-guided radiation therapy.
abstract: OBJECTIVE
  In order to not add extra uncertainty to radiotherapy planning process, accurate margin algorithm is necessary, therefore we propose a centre-shift method to estimate its accuracy.
  
  
  METHODS
  A series of spherical phantoms are used with different CT slice separations (SSs) and pixel sizes (PSs). They are grown by different margins, and displaced geometric centres provide a window on accuracy. Volume difference between pre- and post-expansion is also calculated to double-check the accuracy.
  
  
  RESULTS
  The measured margin nearly varies as multiples of PS in the transaxial plane; in the superior-inferior direction, it is approximately equal to SS when the ideal margin is smaller than SS. A sphere's volume of <1 cm(3) is underestimated by 3-70% for all PSs, and 2-100% for SS of ≤5 mm but overestimated up to 112% for >5 mm. For volumes of >1 cm(3), relative volume error decreases, and it is nearly zero for >100 cm(3). The dependence of margin accuracy on SS and PS is largely eliminated by volume difference method.
  
  
  CONCLUSIONS
  We have proposed a simple method to estimate margin-growing accuracy and suggested corrective action to minimize the variation.
  
  
  CONCLUSIONS
  One big difference from the previous results is that SS and PS both influence the accuracy of margin growth and volume calculation in Eclipse(™) treatment planning system (Varian Medical System, Palo Alto, CA).
authors.affiliation: 1 Department of Radiation Oncology, Chongqing Cancer Institute, Chongqing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: 1 Department of Radiation Oncology, Chongqing Cancer Institute, Chongqing, China.|2 Division of Physics, Chongqing Cancer Institute, Chongqing, China.
authors.forename: Fu
authors.initials: F
authors.lastname: Jin
authors.affiliation: 3 Forensic Identification Center, College of Criminal Investigation, Southwest University of Political Science and Law, Chongqing, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Zhou
authors.affiliation: 2 Division of Physics, Chongqing Cancer Institute, Chongqing, China.
authors.forename: Huanli
authors.initials: H
authors.lastname: Luo
mesh_terms: D000465:Algorithms; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D000072662:Margins of Excision; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden / Q000528:radiation effects