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Complicated radiation question?

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Posted 8/20/2014 5:41 PM (GMT 0)
As I understand it, Cancer cell division is when radiation dosage kicks butt. In other words radiation does not destroy cells until they are in the process of dividing.

BT planning and dosimetry place seeds at strategic locations to target tumors, other areas within the capsule, and up to 5 mm outside the capsule to allow for EPE, ECE, and potential Positive Margins.

How long can cancer cells continue dividing? Considering the half life and diminishing gy of p103, how can one be reasonably assured that the cancer be extinguished?
Posted 8/20/2014 6:31 PM (GMT 0)
Radiation doesn't initially kill the cancer cells. Rather it damages the DNA which then upsets the ability to divide and live. It can take many months and years for the cancer cells to eventually die, which is why PSA reduces slowly following radiation and can take 2-3 years before reaching the low point (nadir).

The general assurance that the cancer has been defeated is when the PSA stays under <.20 for ten years. That is the general definition of cure that many of the leading radiation oncologists use. It is still possible even then that there is cancer left in the body that can still cause problems, but that is not normal.

Different radiation methods deliver different doses and time frames. As you mention, permanent seeds deliver a very low continuous dose over many months. In my case I used HDR brachytherapy which delivered all the very high dose in less than 30 minutes. Generally external beam radiation (IMRT/IGRT) delivers low frequent doses in 25-40 daily fractions (doses) while SBRT and CyberKnife deliver very high doses in only 5 fractions.
Posted 8/20/2014 6:43 PM (GMT 0)
Brown trout,
Chemo works only on cells at the time of division. That's why it is more effective on fast growing cancers than slow growing ones like PC. Radiation works by killing cells. Cancer cells are more susceptible to radiation than normal cells, that' why at the correct dosage normal cells are mostly spared. Radiation also changes the DNA of both normal and cancer cells making normal cells "fallow" or unable to turn into cancer cells in the future. The psa bounce that many patients experience is due to the cancer cells dieing.
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