Log in
Advanced Prostate Cancer
5,962 members5,701 posts

Proton beam vs. x-ray therapy

I was lucky enough to be recommended by Darryl and Malecare (thank you for that) to participate as a "consumer reviewer" for the "Department of Defense, Congressionally Directed Medical Research Programs, Prostate Cancer Research Program". There were about 15 scientists, mainly professors of medicine or molecular biology, and two of us prostate cancer survivors who were there to provide a patient point of view.

It was a fascinating experience that, unfortunately, I can't talk too much about because we were reviewing proprietary proposals by various labs looking for government research funds and we all had to agree to confidentiality provisions that forbid us from saying anything at all about the research proposals we read. However, on the side, at meal times, I asked various scientists for their views on subjects of interest to patients. One question that I asked of two different medical school professors of radiation oncology was, Is proton beam therapy better than x-ray therapy for prostate cancer treatment? I asked the question at two different meals, one with each of the professors, so they didn't hear each other's answers. They were from different universities, but their answers were pretty similar.

I didn't say to the professors that I was planning to publish their statements (and in fact I had no specific plans yet about that) so I don't feel that I have the right to use their names. All I will say is that there were two of them, they were medical school professors and radiation oncologists who are recognized in the field of prostate cancer research, they answered my questions without hearing each other's answers, and I'm giving you what I believe to be an honest and accurate report of what they said.

First of all, both of them said that there is no difference in outcomes. As one professor put it, assuming that the beams are properly aimed, the success of radiation therapy is entirely dependent on the dose administered and it doesn't matter whether the dose is of protons or of x-rays. He said that the dosage levels matter, type of radiation doesn't. Your chance of killing off the cancer is the same with x-rays or with protons.

The other question I asked was, are the side effects different. One professor answered this way: He said that, theoretically, there are reasons for believing that the adverse side effects from proton beam will be less than for x-rays. However, he said, there are no good studies that compare them and we really don't know if the side effects are better.

The other professor answered differently. He also said that there are no studies giving objective evidence, but he doubted that the side effects of proton beam were any better than for x-rays. His reasoning was as follows:

The most sensitive tissues in which "late complications" occur are in the rectal wall and the bladder neck. He drew me a diagram to show that the rectal wall is smack dab up against the back side of the prostate, and the bladder neck is right up against the top of the prostate. He said that, because of their close proximity, there is no way to spare the rectal wall or the bladder neck without also sparing the part of the prostate itself that is up against those other tissues. He therefore thought that proton beam would only spare the rectal wall and the bladder neck if it didn't treat the entire prostate - which risks a worse outcome in killing all the cancer.

I told one of the doctors that I knew a man some years ago whose insurance would not cover proton beam so the man mortgaged his house to raise the $70K to pay for it. The doc was horrified.

Are the two professors right? I'm not qualified to say. However if they are right, then I think the lesson to be learned is: Find the best radiation oncologist - the one who is going to aim the beams or the seeds carefully and right and who is going to give the right dose. The choice of protons vs. photons (x-rays) is irrelevant.

I believe that there has been a lot of hype and a fair amount of advertising puffery by some proton beam therapy centers. One center in the Czech Republic is even advertising a 98% "cure" rate, which I think is a ridiculous and pernicious statement.

For whatever they are worth those are my thoughts on the matter.


5 Replies

Seems that the benefits are mostly theoretical. Here's a blurb from the American Cancer Society:

Proton beam therapy focuses beams of protons instead of x-rays on the cancer. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and release their energy only after traveling a certain distance. This means that proton beam radiation can, in theory, deliver more radiation to the prostate while doing less damage to nearby normal tissues. Proton beam radiation can be aimed with techniques similar to 3D-CRT and IMRT.

Although in theory proton beam therapy might be more effective than using x-rays, so far studies have not shown if this is true. Right now, proton beam therapy is not widely available. The machines needed to make protons are very expensive, and they aren’t available in many centers in the United States. Proton beam radiation might not be covered by all insurance companies at this time.

1 like

That's an interesting statement from the American Cancer Society. My impression is that big organizations like ACS or NCI are extremely careful about what they say. They don't want someone coming to them complaining or suing them for saying something that isn't strictly true. So they'll say things like, "... so far studies have not shown ...", rather than "... doesn't work".



Alan, thank you for the information.



Here is how Myers explained it to me:

Radiation is generally good only if you have 5 or fewer Metastasis.

Here is the hierarchy of increasing ability to focus on smaller targets:

o ‎IMRT (rotates 180 degrees)

o ‎Tomotherapy (rotates 360 degrees, thereby concentrating radiation on a smaller target)

o ‎Cyberknife (rotates in a complete sphere for an even smaller Target)

o ‎Proton beam is able to target an even tighter and smaller Target that cyberknife

1 like

Let me comment a bit on radiation targeting.

Rotation of the x-ray emitter is for the purpose of reducing the dose to areas outside the prostate. Imagine a moving x-ray emitter aimed at the prostate from 20 different positions. The prostate will get 20 doses of radiation, but the areas around the prostate will only get 1 dose each if the beams only cross each other in the prostate itself. You can get the same 20 doses from a single position firing 20 times, but it gives a big 20X dose to everything in the beam's path from the place where it enters the body to the place where it exits - not just to the prostate. You can see the same effect by shining multiple flashlights from different positions onto a single point. The point is brightly lit but the areas behind the point aren't all that bright.

How many different positions do you need to treat the prostate successfully? The answer is, that you need to shine enough x-rays on the cancer to destroy it, but not shine too much on the areas outside the prostate so as to destroy them too. IMRT and the other standard technologies do that. If you've achieved that, adding more radiation positions produces diminishing returns. It doesn't provide any more effective treatment and the side effects have already been minimized.

Proton beam radiation uses a totally different way to put high radiation on the prostate and low radiation elsewhere. It fires from just one or a few points, but the protons deposit almost all their energy in the prostate region (look up "Bragg Peak" for info on how that works), with very little in the tissue before it and even less after.

Also, targeting the prostate is not about getting a tight point. The rad oncs generally try to saturate the entire prostate, which may be the size of a walnut or bigger.

I would say that all of the modern techniques - IMRT, proton beam, Cyberknife, brachytherapy, and a few others - are able to provide enough radiation to the prostate to cure the cancer, and are also able to minimize radiation to the area that should not be radiated so as to prevent serious side effects. I personally think that there are differences in cost and convenience between the different techniques, but all of them work well. The way to get a good outcome is not by trying to pick one technique over another but by picking the best radiation oncologist - someone who will put thought, effort, and commitment into the planning and execution of the radiation therapy.



You may also like...