Well, your prostate isn't mush after radiotherapy. Actually, quite the opposite - it's firm and inelastic due to fibrosis.
Radiotherapy is not like sticking your prostate in the microwave for 10 mins, which is what a lot of people imagine. It's actually very selective for killing the cancer cells or stopping them from being malignant (i.e. can't grow and spread), while leaving the non-cancerous cells untouched.
Cancerous cells became cancerous by getting corruptions in the genes in their DNA. Genes are like little computer programs. If they go corrupt, they won't work anymore or will do something different than intended. Genes actually go corrupt quite frequently, probably daily in each cell's DNA. There are many genes who's job it is to repair different types of corruption in the DNA - you will know of some of them such as BRCA1, BRAC2. However, if one of these genes gets corrupted, then some types of DNA repair are no longer possible in that cell. That's not a problem until some more corruptions happen. If they happen in genes controlling a couple of specific cell functions, then you have cancer. These are the genes responsible for deciding when the cell should divide and multiply, which is a normal function to produce new cells to replace dead ones. However, if that starts running out of control, the cell will be producing lots of replicas of itself, with the same broken genes, and then you have a cancer growing. There's a similar function for cell death (apoptosis). Cells in your body don't normally live to the point of dying of old age, because you'd have lots of old dysfunctional cells - they commit suicide when they're past their prime, so the bulk of cells in your body are in their prime. This is controlled by genes too, and if those genes stop working, then the excess bulk of cancer cells will grow even faster.
So cancer cells typically have 3 mutations - unable to repair gene mutations, dividing and multiplying too fast, and not killing themselves so they do live much longer until they die of old age. Radiotherapy exploits the first of these - unable to repair gene mutations. It generates large amounts of free radicals in the cell, and these generate loads of gene corruptions. Over the next 24h, the gene repair programs run and repair these corruptions. Except, in the cancer genes, not all types of corruption are repairable, in which case the corruptions remain. Next day, another dose of radiotherapy does the same, and again, the healthy cells repair their corrupted genes, but the cancer cells can't and accumulate more gene corruption. As this is repeated, the cancer cell genes are accumulating more and more corruptions, while the healthy cells keep repairing themselves. At the end of the radiotherapy, the intention is that the cancer cells are sufficiently corrupted that the genes which are involved in cell division/multiplication can't work anymore, which means the cell is no longer malignant, and the cancer can't grow or spread anymore.
This is an idealised description. It's not as clean as this though. There is collateral damage to healthy cells too. In order to be pretty sure all the cancer cells are non-malignant by the end, the radiotherapy dose is set so the collateral damage is low enough that enough healthy cells survive to enable the organ to repair itself. That percentage of collateral damage depends on the organ and I don't know what it is for the prostate, but it's probably something along the lines that the prostate can recover providing you don't kill more than, say, 10% of the healthy cells in the process. Radiotherapy dosing is based on getting that balance right - enough to knock out all the cancer, but not enough to kill the prostate or leave large areas necrotic. If you did have large areas of necrotic tissue left, that would result in sepsis and your death as the body would not be able to fight infection there. The prostate has to work well enough afterwards to be able to fight off infection and maintain its tissues.
The repeated radiotherapy and healing cycles generate a lot of scarring and resulting fibrosis as that heals. This makes the organ hard and inelastic which is the main reason it no longer works for producing semen (it's normally soft and muscular), and very likely damage to the ducts too. However, not so much damage that the blood supply is compromised, so the body can still maintain it.
There has been a concept of max lifetime dose to any tissues for almost 100 years since the work of Claudius Regaud in the 1920s, which calculated the dosing and fractionation required to kill cancer cells (although bizarrely he actually did this by working out the dose required to sterilise ram's testicles without permanently damaging their scrotal skin).
It's only relatively recently that we started experimenting with changing his findings, which brought in the shorter treatment sessions using hypofractionation (20 fractions) and ultrafractionation (5 fractions).
It's even more recently that we've considered that after many years of healing, another dose to the same area might be possible, sufficient to kill cancer, but not too many healthy cells. This isn't standard practice in the UK (or anywhere yet as far as I know), but has been done experimentally. The challenge will be to find if there is a balance between doing too much damage and killing the cancer, and that window is probably much smaller and possibly virging on the non-existent for a second treatment to the same area.
Edited by member 02 Oct 2024 at 11:56
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