title: Use of radiation protraction to escalate biologically effective dose to the treatment target.
abstract: OBJECTIVE
  The aim of this study is to evaluate how simultaneously increasing fraction time and dose per fraction affect biologically effective dose for the target (BED(tar)) while biologically effective dose for the normal tissue (BED(nt)) is fixed.
  
  
  METHODS
  In this investigation, BED(tar) and BED(nt) were studied by assuming mono-exponential repair of sublethal damage with tissue dependent repair half-time.
  
  
  RESULTS
  Our results demonstrate that under certain conditions simultaneously increasing fraction time and dose per fraction result in increased BED(tar) while BED(nt) is fixed. The dependence of biologically effective dose on fraction time is influenced by the dose rate. In this investigation we analytically determined time-varying dose rate R̃ which minimizes BED. Changes in BED with fraction time were compared for constant dose rate and for R̃.
  
  
  CONCLUSIONS
  A number of recent experimental and theoretical studies have demonstrated that slow delivery of radiation (known as radiation protraction) leads to reduced therapeutic effect because of increased repair of sublethal damage. In contrast, our analysis shows that under certain conditions simultaneously increasing fraction time and dose per fraction are radiobiologically advantageous.
authors.affiliation: Department of Radiation Oncology, Halifax Health, Daytona Beach, Florida 32114, USA. vadimkuperman@yahoo.com
authors.forename: V Y
authors.initials: VY
authors.lastname: Kuperman
authors.forename: G S
authors.initials: GS
authors.lastname: Spradlin
mesh_terms: D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness