title: On-line localization of the lumpectomy cavity using surgical clips.
abstract: OBJECTIVE
  To present an on-line image guidance procedure for external beam accelerated partial breast irradiation based on cone-beam computed tomography (CBCT) imaging of surgical clips; and to estimate the possible clinical target volume (CTV) to planning target volume (PTV) margin reduction allowed by this technique.
  
  
  METHODS
  Clips in the CBCT image are detected automatically using in-house software. The treatment couch is translated according to the shift in the clips' center of mass between the planning and CBCT images. Three components for the PTV margin are considered: (1) breathing, (2) surrogate error (i.e., error in cavity position after perfect setup to clips), and (3) residual error (i.e., error arising from the inability to execute a perfect setup to clips due to technological limitations, such as couch travel precision). These factors were input into a standard formula for CTV-to-PTV margin calculation.
  
  
  RESULTS
  The average magnitude of clip-based corrections was 7 +/- 2 mm (10 patients, 44 fractions). After localization, the residual error magnitude was 1.6 +/- 1.3 mm, justifying an isotropic CTV-to-PTV margin of approximately 6 mm, including breathing and surrogate error.
  
  
  CONCLUSIONS
  On-line localization of the lumpectomy cavity using surgical clips is technically feasible from the standpoint of equipment, time, and process, making possible a decreased CTV-to-PTV margin for accelerated partial breast irradiation. Because the procedure is exclusively target based, additional monitoring of critical structures may be advisable.
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48703, USA. lkim@beaumonthospitals.com
authors.forename: Leonard H
authors.initials: LH
authors.lastname: Kim
authors.forename: John
authors.initials: J
authors.lastname: Wong
authors.forename: Di
authors.initials: D
authors.lastname: Yan
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D009068:Movement; D009862:Online Systems; D012119:Respiration; D013525:Surgical Instruments