Wednesday, January 27, 2016

Hypoxia and radiotherapy

What effect do you think hypoxia would have on radiotherapy?

Okay I know this. Hypoxia kills cells so it should help right?
I'm afraid you couldn't be more wrong.




There are different mechanisms of radiotherapy induced cell damage
 -DNA breaks by ionisation leading to apoptosis
 -Oxygen dependent free radical generation and DNA damage
Here we only deal with O2.

Effect of oxygen: Oxygen is important for generating and sustaining free radicals.
 radiation effects on cell water  : H20 --> H2O* + e−
                                                H2O* + H2O --> H30* + OH-
                                                OH- causes damage to cell membranes, organelles and proteins.
A lot of radiotherapy induced damage is caused by hydroxyl radicals.
And in the absence of Oxygen these free radicals wouldn't be generated.

So Hypoxic(Oxygen deprived) tissues are relatively resistant to the effects of radiation. In fact it takes 2-3 times,also called as the oxygen enhancement ratio(OER), the radiation dose to induce same damage in a hypoxic tissue than in an oxic tissue.

Recognising the importance of hypoxia, it is important to make sure that patients are not anaemic(<12gm/dl) when they start radiotherapy. Also some trials have demonstrated the benefits of Hyperbaric Oxygen Therapy(HBO) during radiotherapy.

Ohh Oxygen!! What would we do without you?! ;)

Adios :)

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