Hi , I finished 20 fractions of rt 2 months ago, I don’t really understand how the radiation carries on working after your treatment has finished,and also how long does this process last , thanks in advance
Hi Paul1963 I am not medically trained but understand that the RT doesn’t immediately kill cancer cells but the treatment will take weeks or even months to kill the cells. I think that is why fatigue isn’t immediate but builds as your body is fighting the bad guys. Think of it more like helping your body to recognise where the cells are over time and fight the cancer. David
This is a complex question. This is my understanding but don't forget we are not experts. The first point to be made here is that, with the exception of spermatozoa and lymphocytes (among the two most rapidly dividing cells in the body), cancer cells die what is called a mitotic death. This means that the cell dies when it attempts to divide and the radiotherapy breaks the DNA chains so that they can no longer divide and multiply. So, if a cell does not divide, then it does not die, but just sits there. At the same time, if a cell doesn't divide, it also cannot grow and spread. This creates debris which the immune system gets to work on to finish the job off.
For tumors that divide slowly like those in prostate cancer, the mass may shrink over a long, extended period after radiation stops. The median time for a prostate cancer to shrink is about 18 months (some quicker, some slower).
The second issue is how the tumor appears on a radiology scan after radiation. As the tumor cells die and break up, the body's white cells clear the debris and cause an inflammatory process, like a bruise.
This inflammatory reaction can make the mass look larger, but this does not necessarily reflect tumor response or growth. These inflammatory reactions usually subside over time, but it may take a few months to see this on CT scan or even up to a year on MRI. PET scans can indicate tumor activity, but can also show inflammation, so are also not generally accurate in areas treated with radiotherapy until several months have passed.
As the debris is cleared away this can result in the PSA bouncing around a little bit but provided the trend is downwards or remains stable then you know that the radiotherapy is doing its job.
In summary, some types of tumor cells shrink very quickly, and this shrinkage can be seen on a radiology scan. Even if no shrinkage is seen right away, cells may still be dying in response to radiation, sometimes causing an inflammatory response that can even make a mass look larger! Over time after radiation, your oncology team should be watching scans to ensure that tumor masses either shrink or stay the same on CT or MRI scan. A PET scan can be used after radiation to detect residual or recurrent tumor activity and in particular a PSMA PET scan is the most sensitive for this with prostate cancer provided the PSA is above 0.2, but preferably above 0.4/5 as it is more accurate at higher levels.
