title: The effect of radio-adaptive doses on HT29 and GM637 cells.
abstract: BACKGROUND
  The shape of the dose-response curve at low doses differs from the linear quadratic model. The effect of a radio-adaptive response is the centre of many studies and well known inspite that the clinical applications are still rarely considered.
  
  
  METHODS
  We studied the effect of a low-dose pre-irradiation (0.03 Gy - 0.1 Gy) alone or followed by a 2.0 Gy challenging dose 4 h later on the survival of the HT29 cell line (human colorectal cancer cells) and on the GM637 cell line (human fibroblasts).
  
  
  RESULTS
  0.03 Gy given alone did not have a significant effect on both cell lines, the other low doses alone significantly reduced the cell survival. Applied 4 h before the 2.0 Gy fraction, 0.03 Gy led to a significant induced radioresistance in GM637 cells, but not in HT29 cells, and 0.05 Gy led to a significant hyperradiosensitivity in HT29 cells, but not in GM637 cells.
  
  
  CONCLUSIONS
  A pre-irradiation with 0.03 Gy can protect normal fibroblasts, but not colorectal cancer cells, from damage induced by an irradiation of 2.0 Gy and the application of 0.05 Gy prior to the 2.0 Gy fraction can enhance the cell killing of colorectal cancer cells while not additionally damaging normal fibroblasts. If these findings prove to be true in vivo as well this may optimize the balance between local tumour control and injury to normal tissue in modern radiotherapy.
authors.affiliation: Department of Radiation Oncology, Ludwig-Maximilians-University Munich, Marchioninistr, 15, 81377 Munich, Germany. silkeschwarz@gmx.de
authors.forename: Silke B
authors.initials: SB
authors.lastname: Schwarz
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Schaffer
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kulka
authors.forename: Birgit
authors.initials: B
authors.lastname: Ertl-Wagner
authors.forename: Roswitha
authors.initials: R
authors.lastname: Hell
authors.forename: Moshe
authors.initials: M
authors.lastname: Schaffer
mesh_terms: D018929:Cell Culture Techniques / Q000379:methods; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000473:pathology / Q000532:radiotherapy; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage