Written by Dr. Sangamithra, MBBS | 

Medically Reviewed by Dr. Ramya Ananthakrishnan, MD on Jul 28, 2021


The photons and the electrons present in the radiation source ionizes the water molecules producing free radicals (OH radicals), which in turn ionizes the atom present in the DNA molecule. Generally normal cells have excellent repair mechanisms but cancer cells are have diminished ability to repair the damages and hence continue to produce cells with the damage. These cells, which have the damaged DNA, will either die or reproduce slowly.


One major limitation of radiotherapy is that solid tumors can develop resistance to it. This is due to the fact that solid tumors outgrow their blood supply and there is low oxygen environment (hypoxia). The more the tumor is hypoxic the greater is resistance to radiotherapy because fixation of oxygen plays a very important role in causing permanent damage to the DNA.


  1. About Cancer - (http://www.cancerhelp.org.uk/help/ default.asp?page=166)
  2. WHAT IS RADIOTHERAPY? - (http://www.cancernet.co.uk/rxt-what.htm)


nizamzualiz Tuesday, September 25, 2012

There is opinion saying Radiotherapy and Chemotherapy treatment are not actually killing the cancer cells but the cells are kept [or maybe deactivated] for a period of time... It will strike back. At that point of time, we may be able to do the same treatment/s, but the attack usually more severe than the first. Possibly, the patient may have no energy to go through the second episode of treatment (due to age and/or tiredness and/or cost incurred). If you are not lucky, the second cancer will strike due to the treatment itself. So, instead of killing the cancer cells the treatment may create second cancer. Appreciate comments please

faranak Saturday, February 11, 2012

could IMRT done near an organ cause the organ a condition that can not be transplanted if needed?

linac Saturday, July 17, 2010

can i ask what's the difference between conventional fractionated XRT versus stereotactic radiosurgery vs external beam radiation therapy?

ahpeng Friday, April 16, 2010

My skin is itchy and scratches now and then please advise

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