title: Practical use of the extended no action level (eNAL) correction protocol for breast cancer patients with implanted surgical clips.
abstract: OBJECTIVE
  To describe the practical use of the extended No Action Level (eNAL) setup correction protocol for breast cancer patients with surgical clips and evaluate its impact on the setup accuracy of both tumor bed and whole breast during simultaneously integrated boost treatments.
  
  
  METHODS
  For 80 patients, two orthogonal planar kilovoltage images and one megavoltage image (for the mediolateral beam) were acquired per fraction throughout the radiotherapy course. For setup correction, the eNAL protocol was applied, based on registration of surgical clips in the lumpectomy cavity. Differences with respect to application of a No Action Level (NAL) protocol or no protocol were quantified for tumor bed and whole breast. The correlation between clip migration during the fractionated treatment and either the method of surgery or the time elapsed from last surgery was investigated.
  
  
  RESULTS
  The distance of the clips to their center of mass (COM), averaged over all clips and patients, was reduced by 0.9 ± 1.2 mm (mean ± 1 SD). Clip migration was similar between the group of patients starting treatment within 100 days after surgery (median, 53 days) and the group starting afterward (median, 163 days) (p = 0.20). Clip migration after conventional breast surgery (closing the breast superficially) or after lumpectomy with partial breast reconstructive techniques (sutured cavity). was not significantly different either (p = 0.22). Application of eNAL on clips resulted in residual systematic errors for the clips' COM of less than 1 mm in each direction, whereas the setup of the breast was within about 2 mm of accuracy.
  
  
  CONCLUSIONS
  Surgical clips can be safely used for high-accuracy position verification and correction. Given compensation for time trends in the clips' COM throughout the treatment course, eNAL resulted in better setup accuracies for both tumor bed and whole breast than NAL.
authors.affiliation: Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. j.penninkhof@erasmusmc.nl
authors.forename: Joan
authors.initials: J
authors.lastname: Penninkhof
authors.forename: Sandra
authors.initials: S
authors.lastname: Quint
authors.forename: Margreet
authors.initials: M
authors.lastname: Baaijens
authors.forename: Ben
authors.initials: B
authors.lastname: Heijmen
authors.forename: Maarten
authors.initials: M
authors.lastname: Dirkx
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D002985:Clinical Protocols; D019583:Dose Fractionation, Radiation; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D016462:Mammaplasty / Q000379:methods; D015412:Mastectomy, Segmental; D009038:Motion; D056888:Patient Positioning; D011446:Prospective Studies; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D013525:Surgical Instruments; D013997:Time Factors