title: Evaluation of tumor progression and detection of new tumors during repeat Gamma Knife® stereotactic radiosurgery utilizing the co-registration tool in Leksell Gamma Plan®: technical note.
abstract: BACKGROUND
  Repeat Gamma Knife stereotactic radiosurgery (GKSR) procedures are becoming common, especially for brain metastases. It is important to identify tumors requiring treatment at repeat GKSR and it can be challenging to distinguish treated tumors, tumor progression and new tumors. Using the image co-registration tool within the Leksell Gamma Plan software, we developed a technique to aid in the identification of tumors needing treatment.
  
  
  OBJECTIVE
  The objective was to explore a new co-registration technique to identify tumors requiring treatment at repeat GKSR procedures.
  
  
  METHODS
  Ten patients who underwent repeat GKSR for brain metastases were identified. Contrast-enhanced volumetric T1 magnetic resonance images (MRI) from the previous GKSR were co-registered with the new images and the resulting two-color format image was used to evaluate tumor status.
  
  
  RESULTS
  Using the co-registered images, tumors were characterized as: resolved, regressed, stable, larger or new. Overall, 13.6% of tumors completely resolved, 26.2% regressed, 13.1% remained stable, while 7.9% progressed. Thirty-nine percent of tumors were new.
  
  
  CONCLUSIONS
  The co-registration technique makes clinically relevant changes conspicuous on MRI. It distinguishes between tumors potentially requiring treatment and those that have been treated successfully. It can be used with tumors other than metastases and for evaluating tumor response at follow-up.
authors.affiliation: Center for Image-Guided Neurosurgery, Department of Neurological Surgery, University of Pittsburgh Medical Center-Presbyterian, Pittsburgh, Pa., USA.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Monaco
authors.forename: Jagdish P
authors.initials: JP
authors.lastname: Bhatnagar
authors.forename: Yuanguang
authors.initials: Y
authors.lastname: Xu
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Arai
authors.forename: Ajay
authors.initials: A
authors.lastname: Niranjan
authors.forename: M Saiful
authors.initials: MS
authors.lastname: Huq
authors.forename: L Dade
authors.initials: LD
authors.lastname: Lunsford
mesh_terms: D000368:Aged; D001932:Brain Neoplasms / Q000556:secondary / Q000601:surgery*; D001943:Breast Neoplasms / Q000473:pathology / Q000601:surgery*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome