title: Adaptive radiotherapy strategies for pelvic tumors - a systematic review of clinical implementations.
abstract: Introdution: Variation in shape, position and treatment response of both tumor and organs at risk are major challenges for accurate dose delivery in radiotherapy. Adaptive radiotherapy (ART) has been proposed to customize the treatment to these motion/response patterns of the individual patients, but increases workload and thereby challenges clinical implementation. This paper reviews strategies and workflows for clinical and in silico implemented ART for prostate, bladder, gynecological (gyne) and ano-rectal cancers.
  
  
  METHODS
  Initial identification of papers was based on searches in PubMed. For each tumor site, the identified papers were screened independently by two researches for selection of studies describing all processes of an ART workflow: treatment monitoring and evaluation, decision and execution of adaptations. Both brachytherapy and external beam studies were eligible for review.
  
  
  RESULTS
  The review consisted of 43 clinical studies and 51 in silico studies. For prostate, 1219 patients were treated with offline re-planning, mainly to adapt prostate motion relative to bony anatomy. For gyne 1155 patients were treated with online brachytherapy re-planning while 25 ano-rectal cancer patients were treated with offline re-planning, all to account for tumor regression detected by magnetic resonance imaging (MRI)/computed tomography (CT). For bladder and gyne, 161 and 64 patients, respectively, were treated with library-based online plan selection to account for target volume and shape variations. The studies reported sparing of rectum (prostate and bladder cancer), bladder (ano-rectal cancer) and bowel cavity (gyne and bladder cancer) as compared to non-ART.
  
  
  CONCLUSIONS
  Implementations of ART were dominated by offline re-planning and online brachytherapy re-planning strategies, although recently online plan selection workflows have increased with the availability of cone-beam CT. Advantageous dosimetric and outcome patterns using ART was documented by the studies of this review. Despite this, clinical implementations were scarce due to challenges in target/organ re-contouring and suboptimal patient selection in the ART workflows.
authors.affiliation: a Department of Oncology and Medical Physics , Haukeland University Hospital , Bergen , Norway ;
authors.forename: Sara
authors.initials: S
authors.lastname: Thörnqvist
authors.affiliation: a Department of Oncology and Medical Physics , Haukeland University Hospital , Bergen , Norway ;
authors.forename: Liv B
authors.initials: LB
authors.lastname: Hysing
authors.affiliation: b Department of Oncology , Helsinki University Central Hospital , Helsinki , Finland ;
authors.forename: Laura
authors.initials: L
authors.lastname: Tuomikoski
authors.affiliation: c Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark ;
authors.forename: Anne
authors.initials: A
authors.lastname: Vestergaard
authors.affiliation: c Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark ;
authors.forename: Kari
authors.initials: K
authors.lastname: Tanderup
authors.affiliation: c Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark ;
authors.forename: Ludvig P
authors.initials: LP
authors.lastname: Muren
authors.affiliation: d Department of Radiation Oncology , Erasmus MC Cancer Institute , Rotterdam , The Netherlands.
authors.forename: Ben J M
authors.initials: BJ
authors.lastname: Heijmen
mesh_terms: D001918:Brachytherapy / Q000379:methods; D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography / Q000379:methods; D005260:Female; D005833:Genital Neoplasms, Female / Q000532:radiotherapy; D006801:Humans; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D057285:Precision Medicine / Q000379:methods; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy; D057188:Workflow