title: Evaluation of overall setup accuracy and adequate setup margins in pelvic image-guided radiotherapy: comparison of the male and female patients.
abstract: We evaluated adequate setup margins for the radiotherapy (RT) of pelvic tumors based on overall position errors of bony landmarks. We also estimated the difference in setup accuracy between the male and female patients. Finally, we compared the patient rotation for 2 immobilization devices. The study cohort included consecutive 64 male and 64 female patients. Altogether, 1794 orthogonal setup images were analyzed. Observer-related deviation in image matching and the effect of patient rotation were explicitly determined. Overall systematic and random errors were calculated in 3 orthogonal directions. Anisotropic setup margins were evaluated based on residual errors after weekly image guidance. The van Herk formula was used to calculate the margins. Overall, 100 patients were immobilized with a house-made device. The patient rotation was compared against 28 patients immobilized with CIVCO's Kneefix and Feetfix. We found that the usually applied isotropic setup margin of 8mm covered all the uncertainties related to patient setup for most RT treatments of the pelvis. However, margins of even 10.3mm were needed for the female patients with very large pelvic target volumes centered either in the symphysis or in the sacrum containing both of these structures. This was because the effect of rotation (p ≤ 0.02) and the observer variation in image matching (p ≤ 0.04) were significantly larger for the female patients than for the male patients. Even with daily image guidance, the required margins remained larger for the women. Patient rotations were largest about the lateral axes. The difference between the required margins was only 1mm for the 2 immobilization devices. The largest component of overall systematic position error came from patient rotation. This emphasizes the need for rotation correction. Overall, larger position errors and setup margins were observed for the female patients with pelvic cancer than for the male patients.
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland. Electronic address: marko.laaksomaa@pshp.fi.
authors.forename: Marko
authors.initials: M
authors.lastname: Laaksomaa
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland; Department of Medical Physics, Tampere University Hospital (TAUH), Tampere, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Kapanen
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland.
authors.forename: Tapio
authors.initials: T
authors.lastname: Tulijoki
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland; Department of Medical Physics, Tampere University Hospital (TAUH), Tampere, Finland.
authors.forename: Seppo
authors.initials: S
authors.lastname: Peltola
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland; Department of Medical Physics, Tampere University Hospital (TAUH), Tampere, Finland.
authors.forename: Simo
authors.initials: S
authors.lastname: Hyödynmaa
authors.affiliation: Department of Oncology, Tampere University Hospital (TAUH), Tampere, Finland.
authors.forename: Pirkko-Liisa
authors.initials: PL
authors.lastname: Kellokumpu-Lehtinen
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; 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*; D016896:Treatment Outcome
keywords: Pelvis; Radiotherapy; Setup errors; Setup margins