Radiation Induced Bystander Effect

Document Type: Review Article

Authors

1 Ph.D Student in Medical Physics Research Center, Bu-Ali Research Institute, Mashhad University of Medical Sciences, Mashhad, Iran

2 Professor, Medical Physics Research Center, Bu-Ali Research Institute, Mashhad University of Medical Sciences, Mashhad, Iran

Abstract

Introduction: Radiation effects observed in cells that are not irradiated are known as non-targeted effects. 
Radiation induced bystander effect (RIBE) as a kind of non-targeted effect has been introduced in recent 
years.  RIBE  occurs  in  unexposed  cells  which  are  related  to  adjacent  or  distant  irradiated  cells.  RIBE 
contradict with "target theory" which necessitates radiation traversal through the nucleus for affecting cells. 
Methods:  To  understand  this  phenomenon,  some  investigations  and  review  articles  which  deal  with  this 
subject were studied. Most investigators have applied in vitro experimental methods to investigate RIBE in 
animal or human cells, but in vivo experiments are also increased in recent years. 
Results: Both low and high LET radiation cause RIBE. Cell responses to RIBE are including: cell death, 
chromosomal  damage,  mutagenesis,  neoplastic  transformation,  genomic  instability,  cell  cycle  delay, 
modification  of  gene  expression  and  radiosensitivity  alteration.  At  low  doses  that  only  some  cells  are 
irradiated this phenomenon is significant. However RIBE exists at high doses, due to predomination of direct 
radiation effects it  is less considered. There is link between RIBE and other non-targeted effects such  as 
adaption and genomic instability. 
Conclusion: At low doses, there is no linear relationship between outcome and the number of cells hit by 
radiation. Thus this will affect the basic principle of defining dose limits which have been initiated by linear 
no  threshold  curve.  There  is  a  scope  to  exploit  RIBE  in  radiotherapy,  and  also  it  is  important  to  avoid 
undesirable bystander effects in normal tissues. 

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Volume 5, Issue 3,4
November and December 2008
Pages 95-110
  • Receive Date: 09 February 2008
  • Revise Date: 28 February 2008
  • Accept Date: 05 March 2008