[ RadSafe ] Abstract: Cellular response to modulated radiation fields (and the bystander effect)

[John Jacobus]

I thought this might be of interest.
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*Physics in Medicine and Biology* 
Volume 52, Number 18, 21 September 2007 (5469-5734,
N393-N424) 
http://www.iop.org/EJ/toc/-alert=1462/0031-9155/52/18 

    Cellular response to modulated radiation fields 
    E Claridge Mackonis, N Suchowerska, M Zhang, M
Ebert, D R McKenzie and M Jackson 
    2007 Phys. Med. Biol. 52 5469-5482 
    Abstract: 
http://www.iop.org/EJ/abstract/-alert=1462/0031-9155/52/18/001

    Full text PDF:
http://www.iop.org/EJ/article/-alert=1462/0031-9155/52/18/001/pmb7_18_001.pdf


    Cell survival following exposure to spatially
modulated beams, as created by intensity-modulated
radiotherapy (IMRT), is investigated. In vitro
experiments were performed using malignant melanoma
cells (MM576) exposed to a therapeutic megavoltage
photon beam. We compared cell survival in modulated
fields with cell survival in uniform control fields.
Three different spatial modulations of the field were
used: a control 'uniform' field in which all cells in
a flask were uniformly exposed; a 'quarter' field in
which 25% of cells at one end of the flask were
exposed and a 'striped' field in which 25% of cells
were exposed in three  parallel stripes. The cell
survival in both the shielded and unshielded regions
of the modulated fields, as determined by a clonogenic
assay, were compared to the cell survival in the
uniform field. We have distinguished three ways in
which cell survival is influenced by the fate of
neighbouring cells. The first of these (type I effect)
is the previously reported classical Bystander effect,
where cell survival is reduced when communicating with
irradiated cells. We find two new types of Bystander
effect. The type II effect is an observed increase in
cell survival when nearby cells receive a lethal dose.
The type III effect is an increase in the survival of
cells receiving a high dose of radiation, when nearby
cells receive a low dose. These observations of the
Bystander effects emphasize the need for improved
radiobiological models, which include communicated
effects and account for the effects of modulated dose
distribution. 

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"If you guard your toothbrushes and diamonds with equal zeal, you'll probably lose fewer toothbrushes and more diamonds."
- Former national security advised McGeorge Bundy
-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com


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