[ RadSafe ] Abstract:: Effect of dose rate on the radiation-induced bystander response

[John Jacobus]

Effect of dose rate on the radiation-induced bystander response
    M D Gow, C B Seymour, Soo-Hyun Byun and C E Mothersill
    2008 Phys. Med. Biol. 53 119-132
    Abstract:
http://www.iop.org/EJ/abstract/-alert=1462/0031-9155/53/1/008
    Full text PDF:
http://www.iop.org/EJ/article/-alert=1462/0031-9155/53/1/008/pmb8_1_008.
pdf

    Radiation-induced biological bystander effects have become a well-established phenomenon associated with the interaction of  radiation with cells. These so-called bystander effects have been seen across a variety of end points for both high and low linear energy transfer  (LET) radiations, utilizing a variety of dose rates and radiation sources. In this study, the effect of dose rate and different low LET sources on  the bystander cell survival fraction (SF) was examined. The cell line investigated was the human keratinocyte HPV-G. The bystander response was measured via clonogenic assay after medium transfer protocol. Cells were irradiated using 60Co γ-rays and 20 MeV electrons at doses of 0.5, 5 and 10 Gy with varying dose rates. Both γ and electron irradiation decreased recipient SF at 0.5 Gy and 5 Gy, respectively. Subsequent recovery of the SF to control levels for 10 Gy was observed. There was no dose rate dependence for 60Co irradiation. A significant
 difference in the survival fraction was observed for electron irradiation at 10 Gy and a high dose rate. Furthermore, survival fractions were compared between 60Co and 20 MeV electron irradiations. This showed a significant increase in the survival fraction 'recovery' at 10 Gy for a 60Co dose rate of 1.1 Gy min-1 compared to 20 MeV electrons at 1.0 Gy min-1. No such difference was observed when comparing at higher dose rates. Lastly, increases in survival fraction at 10 Gy were abolished and the SF decreased by the plating of increased numbers of recipient cells. Such evidence may help gain insight into  the nature and mechanism(s) surrounding bystander signal production, how these phenomena are tested and their eventual application in a clinical setting.


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"If history teaches any lesson it is that no nation has an inherent right to greatness.  Greatness has to be earned and continually re-earned."
- Norman Augustine, Chairman of the National Academies Committee 

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com
       
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