For how long does radiation have a cytotoxic effect on prostate cancer cells?

I was wondering about the duration of the cytotoxic effects of various forms of radiation therapy on prostate cancer cells?

Does anyone know for example how hypofractionation delivery methods like CK and HD brachytherapy kill cancer cells during treatment and how rapidly the killing of cancer cells tails off after treatment stops?

Does most of the cytotoxic effect happen during the treatment itself and then drops off quickly after treatment or do the cells continue to be killed off for weeks afterwards?

When radiation fails, it's usually because the cancer cells escaped being radiated. The micro-mets, impossible to detect, had already left the barn...

Cytotoxic therapy includes any agent that is toxic to the cell and attempts to kill the cell. The agent can be chemical, molecular, immuno, etc. Thus, radiotherapy is considered to be a cytotoxic agent.

Hormone therapy is not considered to be cytotoxic as it is intended to control, not kill the cancer. Some doctors contend, Meyers for example, that HT does do some killing, but not in the same way or same rate that cytotoxic treatments like chemo and radio therapies do.

In professional literature, radiotherapy is cited as being cytotoxic, though, as Andrew points out, it isn't normally referred as such in more casual settings like Healing Well..

Actually, PCa can survive HT and stay dormant for a very long time, usually in the ends of bones. That is why we see often see cancer recurrence many years after the treatment has ended. As PCa becomes hormone refractory it actually helps develop its own food to continue to live, divide and grow in spite of having no testosterone to feed on. We wish that HT would solve the problem, but many times the cancer is not adequately affected.

Hoping,

Many of the cancer cells are destroyed immediately by the radiation. Radiation interacts with water and oxygen to form what is called "Reactive Oxygen Species (ROS)", which are mostly hydroxyl radicals. The ROS disrupt a wide range of cellular processes, causing cell death. Those cells that survive immediate killing have what is called "double strand breaks" in their DNA from the hydroxyl radicals. When the cell tries to replicate the DNA, it can't, and dies. Some of the cancer cells go into stasis and may take years to try to divide. Eventually they will try, and they die.

Some healthy cells are also killed immediately by the radiation but are quickly replaced (in a matter of hours) by fresh ones. However, healthy cells have survival mechanisms that cancer cells lack. They can often self-repair the ROS damage. When faced with damage they can't repair, they initiate "apoptosis" (suicide), and are replaced by their brethren. (Cancer cells typically lack the ability to undergo apoptosis). Dose is limited in order to prevent damage to healthy cells.

There is also a secondary effect on the immune system. All those exploding cancer cells release cell surface proteins (antigens) that are detected by T cells. They create "killer T cells" that hunt down and destroy any cancer cells they detect that express those antigens. This is called "the abscopal effect" or the "bystander effect."

It's the genetic differences between cancer cells and healthy cells that allows radiation to cure the cancer without a lot of damage to healthy cells.

- Allen

HopingForTheBestinNJ said...

Are DRE's still something that should be done regularly after completing radiation treatments or only PSA? Does the prostate feel different, "post toastie" ?

DRE's still happen. While having a DRE with my radiation oncologist prior to my procedure I asked if at least being treated meant that I no longer needed to have DRE's? Not the case. We still need them done. Don't know how they feel different. If any MD's are on board they can chime in.

Thanks to all for the information!
Allen - thanks for the excellent explanation of how the process works!

Works Out said...
DRE's still happen. While having a DRE with my radiation oncologist prior to my procedure I asked if at least being treated meant that I no longer needed to have DRE's? Not the case. We still need them done. Don't know how they feel different. If any MD's are on board they can chime in.

Works Out, My Uro hasn't done a DRE since I had my HDR brachy treatment almost 2 years ago. I haven't asked him about it, and I don't intend to!

Well - it's not by my choice!

Those who did my treatment (same people as did yours) told me I should be doing it, though my Uro suggested skipping it at my 9 month follow up. My 1 year follow up with him, and also my annual with my PCP, is coming up in a few weeks and expect I'll have a DRE done with one of them.

I see your PSA is trending nicely down (congrats) . If I can show similar numbers I'll push to drop future DRE's.

Hawaii-Guy said...

Works Out said...
DRE's still happen. While having a DRE with my radiation oncologist prior to my procedure I asked if at least being treated meant that I no longer needed to have DRE's? Not the case. We still need them done. Don't know how they feel different. If any MD's are on board they can chime in.

Works Out, My Uro hasn't done a DRE since I had my HDR brachy treatment almost 2 years ago. I haven't asked him about it, and I don't intend to!