Originally Posted by: Online Community MemberI'm no expert. My basic understanding is that EBRT destroys all cells it comes into contact with. The important thing is that the healthy cells killed will regenerate. For some reason, which remains a mystery to me, the cancerous cells won't. Once they're dead they're dead in other words.
The RT is not intended to destroy cells. A necrotic prostate would be a seriously life threatening condition.
The RT exploits a property of cancer cells, in that they became cancer cells because their DNA got corrupted and they failed to repair it. Cell DNA gets regularly corrupted, so cells have a variety of ways of correcting it depending on the corruption. While the DNA is corrupt, the cell disables dividing and multiplying (which is its reproduction mechanism, although reproduction is the wrong word). Cancer cells generally have 4 faults, 1) the DNA is corrupt, 2) the DNA repair mechanism isn't working, 3) the corruption is not bad enough to prevent the cells dividing and multiplying, 4) the programmed cell death (apotosis) which happens in healthy cells before a cell reaches old age stops working.
The radiotherapy sets about to corrupt the DNA in all the cells, mainly by splitting water molecules into highly reactive free radicials, which react with parts of the DNA chain, corrupting it. Healthy cells will invoke their DNA repair mechanism and repair this damage. Cancer cells generally can't do this because their DNA repair mechanism is broken. Then next day, you hit them all with another round of RT. This corrupts all the DNA again, and healthy cells repair their DNA again. Cancer cells couldn't, and now have two lots of corruptions to their DNA. As the RT continues over time, you can see that damage is cumulative in the cancer cells, but the healthy cells are repairing themselves each time. By the end of the radiotherapy, the cumulative damage to the cancer cells should be enough to make them incapable of dividing and multiplying any more, i.e. they're no longer malignant. They may not be dead yet, and can take a couple of years to die, but providing they can no longer multiply, the cancer cannot grow and spread, and eventually all the cancer cells will die of old age.
This is why (if you aren't on HT) it takes time after the RT for the PSA to drop to a minimum as the cancer cells die over that period. The prostate is capable of some regeneration. So, as the cancer cells die, some will be replaced with healthy cells, and PSA will likely rise a bit. You can get PSA bounces, and this is thought to be due to your immune system occasionally spotting there are a lot of dying cancer cells and attacking them, although the cause of PSA bounces isn't well understood.
The RT does also cause collateral damage to some healthy cells, and this is what causes the various RT side effects.