title: BED-time charts and their application to the problems of interruptions in external beam radiotherapy treatments.
abstract: OBJECTIVE
  The use of radiobiological modelling to examine the likely consequences of interruptions to radiotherapy schedules and to assess various compensatory measures.
  
  
  METHODS
  An effect-time graphical display, the BED-time chart, has been developed using the linear-quadratic (LQ) model. This is used to examine the effects on tumour and normal tissues of treatment interruption scenarios representative of clinical situations. The mathematical criteria governing successful salvage have also been drafted and applied to typical situations.
  
  
  RESULTS
  The successful salvage of an interrupted treatment is dependent on a number of interacting factors and the method presented here can be used to examine the trade-offs that exist. Although the mathematics may be complex, it is shown that the dilemmas posed by an interrupted treatment may be more easily appreciated with reference to BED-time charts. These may therefore have a useful role as a teaching aid for portraying a wider variety of radiotherapy problems and also in the documentation of interruptions to treatment and the measures taken to compensate for them.
  
  
  CONCLUSIONS
  Interruptions to radiotherapy regimes are undesirable and compensatory measures need to be initiated as soon as possible after the gap, with a view to completing the amended treatment within the originally prescribed treatment time. Adequate compensation is particularly difficult for long gaps and gaps which occur towards the end of the scheduled treatment. Modelling exercises can help establish guidelines on the available windows of opportunity.
authors.affiliation: Department of Radiation Physics and Radiobiology, Hammersmith Hospitals NHS Trust, London, United Kingdom.
authors.forename: J A
authors.initials: JA
authors.lastname: Sinclair
authors.forename: J P
authors.initials: JP
authors.lastname: Oates
authors.forename: R G
authors.initials: RG
authors.lastname: Dale
mesh_terms: D000465:Algorithms; D019583:Dose Fractionation, Radiation; D016014:Linear Models; D009369:Neoplasms / Q000532:radiotherapy; D011853:Radiobiology; D012062:Relative Biological Effectiveness; D016879:Salvage Therapy; D013997:Time Factors