Protons 101: What is Proton Therapy?

On a basic level, this is always the first question I get when asked why I moved to Oklahoma – What is Proton Therapy? So today, I’ll try to give a balanced look at why they are better and why, even with that statement, why they aren’t for every case:

Breakdown of Proton Therapy

In simple terms, it is the fanciest external radiation treatment.

Proton Therapy is using a beam of protons – the positive charged particle that makes up the center of an atom of Hydrogen (back to middle school science days) to treat cancer. This kind of radiation is only given in 30 total centers in the US. This represents less than 3% of the current radiation machines.

In contrast, External Beam Photon treatment uses electromagnetic radiation. This covers everything from a dental x-ray, to a mammogram, to chest x-rays, to CT scans, to radiation treatment for cancer. They all are similar, the radiation for cancer treatment is just a lot higher energy and a lot more of it than those used for imaging.

These are the two external radiation options. If your not at an advertised Proton Center, your radiation is photon beam external radiation treatment. Here is a map of current US facilities (outside link to NAPT map).

So what is the difference….

External beam photon treatment goes through the entire body and exits the other side of you. Think of an x-ray, they put the film on the other side of the body from the source. For a chest x-ray the beam enters the back and the film is in front of your chest. The film “sees” differences in what exits through your body.

Two main differences between Proton Therapy and external beam radiation:


That is the main difference on a basic level.


With external photon treatment you don’t change where the dose gets delivered for the beams – they generally deposit most energy pretty close to the skin (within an 1-2 inches) and then deliver less dose as they travel across the body. Protons deliver a lower dose on entry and then drop most of the dose within the target.

Is Proton Therapy the Better Treatment?

Yes and no.

From a physics standpoint, it is better. The two items above give us more opportunity to hit the target and miss other stuff. So Yes.

But it is not a fix all – I don’t want anyone to read this and think Proton Therapy is the magical fix for their cancer. What I do think is that for about 2% of cancers is a absolutely critical component of treatment. Next, there is another 3-5% or so where the doses given with Proton Therapy simply aren’t given outside of Proton Centers or the tumor is so close to critical structures that traditional doses aren’t achievable without the benefits of Proton Therapy . So a core of about 5-7% of cases where it is a very important (many would say critical) component of standard high quality treatment – IF you have access to them.

But beyond that small segment, there is a ever increasing percentage of patients, let’s say 1/3 to 1/2 of cancer patients (nearly the entire IMRT, SBRT, SRS patient population) where Proton Therapy has the opportunity to significantly improve the plan and reduces dose to normal tissue. With that improvement comes the opportunity to cause less side effects and improve outcomes. This large patient group is the patient segment that had me move my practice here to Oklahoma Proton.

Proton Therapy: A Physician’s Opinion

I strongly believe proton therapy will be the standard of care for an ever increasing percentage of patients over the next decade.

Proton facilities in the past have been incredibly expensive to build (they still are really expensive, generally) and treatments have been historically very high priced. External photon beam facilities continue to improve and with a 30 – 1 market share over Proton Facilities, they are very refined and efficient processes that deliver great care. For some patients, however, the improvement in plans from IMRT to Proton Therapy is massive from my perspective. For some patients, there is far less benefit and for some patients the treatments could be much more complicated due to differences in skin dose, matching fields, technical delivery issues, changes in density, range uncertainty issues etc. Add those together, today, the best answer might very well may be IMRT or SRS or SBRT for you and your cancer.

But I really believe over the next 5-10 years, as technology within the Proton Facilities improves and we see improved access to Proton Therapy, this balance of who benefits with Proton Therapy will shift dramatically from IMRT as the “standard complex modality” of today to Proton Therapy as the “standard complex modality” of tomorrow. More and more, as Proton Facilities integrate the efficiencies and imaging and new technologies that are currently widespread in the photon world, the gap between Proton Therapy and IMRT will become more and more clear.

So if I am diagnosed with cancer, what do I do?

I think step one is to become educated – at least a bit. In the ideal world, this shouldn’t be required as much but when your are dealing with a relatively uncommon resource, I think you have to educate yourself more than when treatment options are common-place.

I think the second step in today’s healthcare environment is to get a formal opinion about whether or not your cases benefits from Proton Therapy. As a simple rule, if you are looking at IMRT, SRS, or SBRT options – asking to be evaluated for Proton Therapy is very appropriate. It won’t be better in all of these cases and it will depend on the experience and equipment on both the photon side and Proton Therapy side, but it is a very appropriate to see if Proton Therapy can improve your cancer treatment plan.


Logistically, this often hard due to access issues. The very large majority of radiation oncologists don’t have access to Proton Therapy and have never even planned a Proton treatment. Financial interest line up on both sides of this question and too often, patients get placed in the middle. But from a decision making standpoint of “Is Proton Therapy better for my cancer?”, I don’t think there is a better answer than running side by side comparison plans. If Proton Therapy affords you benefits, then we’ll show you plans to demonstrate the difference. If it doesn’t offer any benefit or isn’t appropriate, we’ll explain why and we’re happy to help coordinate care for your cancer journey in whatever way we can help.

On this site, we’ll continue to slowly go site by site and example by example to build information so that more and more people can see where it can help and how it benefits patients in those cases.

I hope this gives you a bit of general context. It’s a bit of a muddy picture, but I think that represents the reality of where we are today.

Dr. Mark Storey MD
Medical Director, Oklahoma Proton Center