title: Set-up uncertainty during postmastectomy radiotherapy with Segmented Photon Beams Technique.
abstract: OBJECTIVE
  To verify the reproducibility of patients irradiated after mastectomy on the immobilization system designed and manufactured for our hospital and to compare the Internal Protocol (IP) with the modified-No Action Level Protocol.
  
  
  BACKGROUND
  Application of forward IMRT techniques requires a good reproducibility of patient positioning. To minimize the set-up error, an effective immobilization system is important.
  
  
  METHODS
  The study was performed for two groups of 65 each. In the first group, portal images for anterior field were taken in 1-3 fractions and, subsequently, three times a week. In this group, the mNAL protocol was used. In the second group, the IP was used. The portal images from the anterior field and from the gantry 0 were taken during the 1-3 and 10 fractions. In both groups, image registration was performed off-line. For each group the systematic and random errors and PTV margin were calculated.
  
  
  RESULTS
  In the first group the value of the population systematic errors and random errors were 1.6 ± 1.6 mm for the left-right, and 1.5 ± 1.7 mm for the cranial-caudal directions, respectively, 1.7 ± 1.3 mm, and 1.9 ± 1.3 mm for the second group. The PTV margins for the left-right and cranial-caudal directions were 5.1 and 4.9 mm for the first group and 5.4 and 6.4 mm for the second group.
  
  
  CONCLUSIONS
  For patients immobilized with our support device treated according to the mNAL protocol or IP, a good set-up reproducibility was obtained. Implementation of IP limits the number of required images.
authors.affiliation: Department of Medical Physics, Maria Skłodowska Curie Memorial Center-Institut, Wawelska 15, Warszawa, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Semaniak
authors.affiliation: Department of Medical Physics, Maria Skłodowska Curie Memorial Center-Institut, Wawelska 15, Warszawa, Poland.
authors.forename: Paweł
authors.initials: P
authors.lastname: Kukołowicz
keywords: Patient positioning; Random error; Systematic error