title: Low-dose radiation hyper-radiosensitivity in multicellular tumour spheroids.
abstract: OBJECTIVE
  We propose and study a new model aimed at describing the low-dose hyper-radiosensitivity phenomenon appearing in the survival curves of different cell lines.
  
  
  METHODS
  The model uses the induced repair assumption, considering that the critical dose at which this mechanism begins to act varies from cell to cell in a given population. The model proposed is compared with the linear-quadratic model and the modified linear-quadratic model, which is commonly used in literature and in which the induced repair is taken into account in a heuristic way. The survival curve for the MCF-7 line of human breast cancer is measured at low absorbed doses and the uncertainties in these doses are estimated using thermoluminiscent dosemeters.
  
  
  RESULTS
  It is shown that these multicellular spheroids present low-dose hyper-radiosensitivity. The new model permits an accurate description of the data of two human cell lines (previously published) and of the multicellular spheroids of the MCF-7 line here measured.
  
  
  CONCLUSIONS
  The model shows enough flexibility to account for data with very different characteristics and considers in a faithful way the hypothesis of the repair induction.
authors.affiliation: Radiophysics Service, University Hospital San Cecilio, Granada, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Guirado
authors.forename: M
authors.initials: M
authors.lastname: Aranda
authors.forename: M
authors.initials: M
authors.lastname: Ortiz
authors.forename: J A
authors.initials: JA
authors.lastname: Mesa
authors.forename: L I
authors.initials: LI
authors.lastname: Zamora
authors.forename: E
authors.initials: E
authors.lastname: Amaya
authors.forename: M
authors.initials: M
authors.lastname: Villalobos
authors.forename: A M
authors.initials: AM
authors.lastname: Lallena
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy*; D049108:Cell Enlargement / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008954:Models, Biological; D011836:Radiation Tolerance; D011879:Radiotherapy Dosage; D018874:Spheroids, Cellular / Q000528:radiation effects*; D014407:Tumor Cells, Cultured