title: Increasing frequency of reirradiation studies in radiation oncology: systematic review of highly cited articles.
abstract: OBJECTIVE
  Identification of the most influential scientific publications and directions of mainstream reirradiation research.
  
  
  METHODS
  A systematic search of the database Scopus (Elsevier B.V., www.scopus.com) was performed, which focused on the time period 1998-2010. Patterns of citation were analysed (total number of citations accumulated independently of their origin and proportion of highly cited articles, arbitrarily defined as those with ≥50 citations).
  
  
  RESULTS
  Up to 64 articles were published each year. Numbers increased over time, especially after the year 2007. Among all 76 articles with at least 50 citations, 28 (37%) focused on head and neck cancer, 27 (36%) on brain tumours including metastases, and 5 (7%) on bone metastases. Most articles evaluated external beam approaches while 10 (13%) focused on brachytherapy. Many of the often quoted publications reported on stereotactic and/or intensity-modulated radiotherapy. Two (3%) reported on randomised clinical studies and 10 (13%) on non-randomised prospective clinical studies (single institution or cooperative group). Only two articles (3%) reported on experimental animal studies.
  
  
  CONCLUSIONS
  The number of published reirradiation studies has increased in recent years. Many studies examined highly conformal and precise radiotherapy, in particular of brain and head and neck tumours. Given that few randomised clinical trials were published, efforts to increase this type of research activity are warranted.
authors.affiliation: Department of Oncology and Palliative Medicine, Nordland Hospital 8092 Bodø, Norway ; Institute of Clinical Medicine, Faculty of Health Sciences, University of Tromsø 9038 Tromsø, Norway.
authors.forename: Carsten
authors.initials: C
authors.lastname: Nieder
authors.forename: Nicolaus H
authors.initials: NH
authors.lastname: Andratschke
authors.forename: Anca L
authors.initials: AL
authors.lastname: Grosu
keywords: Radiotherapy; citation; radiation oncology; radiation retreatment; reirradiation; research evaluation