Proton vs Photon

@jesse65 Great info and analysis and you leave me with a question I never considered.
If protons, by their nature, omit the EXIT release of energy, what about the ENTRANCE release? ie: those protons that released maximum energy before reaching their target?
It seems that you might have the same issues, but just in different areas.
Phil

I was recently diagnosed September 2025 . Drs and research studies all said the same thing - survival rates are statistically the same with all modes: photon, proton, or surgery. The big difference is in the side effects and quality of life. For me, my priority consideration for choosing a treatment was long-term quality of life, particularly given the difficult struggles my dad had with debilitating urinary strictures from his prostate radiation - didn't show up until 20 years after his treatment. (I know times are different and much more advanced, but that surplus radiation dose to normal cells is on all our minds)

I did a lot of deep research, as many of you have, and was 100% settled on Proton Therapy. It made intuitive sense to me, if you cut out the exit dose, you are cutting out half the risk to normal tissue. The predictable distance that protons travel surely makes it more precise. I followed up with visits to three different proton centers: Mayo Phoenix and Wash U St. Louis have all modes of RT; and I also visited a private Proton Center. Neither Wash U nor Mayo recommended Proton Beam for me. I leaned in to each and told them I was specifically looking for Protons, why didn't they want to sell them to me? I'm not a doctor and this is my own interpretation of what I heard:

Proton Beams are very precise in the maximum distance they travel before releasing all their energy. However, not all protons travel the maximum and may not reach that target, leaving unanswered questions about the evenness of the treatment exposure and the actual dose received in any one specific spot. Second, when a Proton release its energy, it releases it in a little cloud, the behavior and width of which is still unknown. Proton therapy has been around since the 60s I believe, but the actual physics of protons in the body is still a bit of a mystery. By comparison, the physics and behavior of light waves (Photons, X-rays, EBRT) has been studied for centuries and its behavior is well known. The edges of the radiation beam are very precise and there is no scatter from release because they pass completely through your body. The radiation energy is relatively low risk from any single one of the EBRT beams, but they are quite potent where the multiple beams all intersect at a pinpoint, and this point of intersection is painted in 3D throughout the Prostate similar to how Proton Therapy is described. Again, I am not a doctor or physicist, just a guy doing his own research.

Studies show that side effects, curability, and longevity are similar for all modes of treatment and I may place the above discussion into the category of me over-thinking and over-analyzing. However, in my case where my lesion is very close to my bladder sphincter, I ended up choosing the precise edge of a photon beam over the the precise distance a photon can travel. With the relatively recent introduction of adaptive therapy techniques, I felt that achieving my goal of reducing risk to my long-term quality of life would be better with photons and adaptive therapy. I start my IMRT treatments in a couple of weeks.

Everyone is different, every situation is different, everybody's goals and priorities are different. I hope I'm not preachy, just trying to share my personal experience. We are lucky to live in a time that can offer a wide variety of treatments with high success rates, but it is unfortunate that us non-doctors are left to make our own treatment decision. There is no wrong decision, only what's right for you. I hope you find this useful.

—> What is the disagreement regarding his MRI?

(During April-May 2021 (at 65y/o), for a localized, PSA of 7.976, Gleason 7(4+3) prostate cancer (with no other known risk factors from MRI or biopsy), I chose 28 sessions of proton beam radiation (at 2.5 grays per session) + 6 months (two 3-month injections) of Eligard + SpaceOAR Vue. For me, successful treatment and quality if life were equal priorities.)

Recent clinical trials (COMPPARE & PARTIQoL) show similar tumor control rates and patient-reported quality of life outcomes when comparing proton vs photon. However, as with all clinical trials, it’s difficult to extrapolate from large population results to how a treatment will impact a specific individual.

With statistically equivalent outcomes, insurance companies sometimes have an impact on that decision (given the much greater cost of proton over photon).

Another issue has to do with access. With only 47 active proton centers in the U.S. (https://proton-therapy.org/findacenter/), scheduling photon is often much easier.

Ultimately, it was the science of proton’s Bragg-Peak characteristics (see attached graphic) that persuaded me to use proton (and the fact that Medicare fully covered it, and that there was a top proton center just a 40-minute drive from my home, all helped my decision immensely).

So, I chose a proton center that was (1) a teaching hospital, (2) a research hospital, and (3) a pediatric radiation center that also did adult radiation. My thinking was that if they can hit a pea-sized tumor deep in a kids’ brain with protons and not cause any surrounding brain tissue injury, they can certainly hit a walnut-size gland and not cause any surrounding tissue injury. (All I have to do is to lay still!)

As is typical for me - despite my confidence that proton radiation was the right choice for me - I hedged my decision by still using SpaceOAR Vue.

I’m not sure why proton radiation works so much better than photon with other types of cancer treatments, and wonder if the laws of quantum physics change for prostate cancer? Or does patient compliance play a role in the outcome?

Anyway, those were my thoughts on the proton vs photon option. My radiation oncologist left the choice up to me. So far, nearly 5 years later, the outcome has been as benign as expected. (Most recent PSA was 0.314.)

If you are considering radiation, I have a list of questions that you might want to ask the radiation oncologist that may help in your decision.

Here’s a presentation on proton radiation (by Dr. Rossi) from the 2023 Mid-Year PCRI conference: https://www.youtube.com/live/WTqPnSRYtW4
—> Starting at 3:38:45

—> What is the disagreement regarding his MRI?

(During April-May 2021 (at 65y/o), for a localized, PSA of 7.976, Gleason 7(4+3) prostate cancer (with no other known risk factors from MRI or biopsy), I chose 28 sessions of proton beam radiation (at 2.5 grays per session) + 6 months (two 3-month injections) of Eligard + SpaceOAR Vue. For me, successful treatment and quality if life were equal priorities.)

Recent clinical trials (COMPPARE & PARTIQoL) show similar tumor control rates and patient-reported quality of life outcomes when comparing proton vs photon. However, as with all clinical trials, it’s difficult to extrapolate from large population results to how a treatment will impact a specific individual.

With statistically equivalent outcomes, insurance companies sometimes have an impact on that decision (given the much greater cost of proton over photon).

Another issue has to do with access. With only 47 active proton centers in the U.S. (https://proton-therapy.org/findacenter/), scheduling photon is often much easier.

Ultimately, it was the science of proton’s Bragg-Peak characteristics (see attached graphic) that persuaded me to use proton (and the fact that Medicare fully covered it, and that there was a top proton center just a 40-minute drive from my home, all helped my decision immensely).

So, I chose a proton center that was (1) a teaching hospital, (2) a research hospital, and (3) a pediatric radiation center that also did adult radiation. My thinking was that if they can hit a pea-sized tumor deep in a kids’ brain with protons and not cause any surrounding brain tissue injury, they can certainly hit a walnut-size gland and not cause any surrounding tissue injury. (All I have to do is to lay still!)

As is typical for me - despite my confidence that proton radiation was the right choice for me - I hedged my decision by still using SpaceOAR Vue.

I’m not sure why proton radiation works so much better than photon with other types of cancer treatments, and wonder if the laws of quantum physics change for prostate cancer? Or does patient compliance play a role in the outcome?

Anyway, those were my thoughts on the proton vs photon option. My radiation oncologist left the choice up to me. So far, nearly 5 years later, the outcome has been as benign as expected. (Most recent PSA was 0.314.)

If you are considering radiation, I have a list of questions that you might want to ask the radiation oncologist that may help in your decision.

Here’s a presentation on proton radiation (by Dr. Rossi) from the 2023 Mid-Year PCRI conference: https://www.youtube.com/live/WTqPnSRYtW4
—> Starting at 3:38:45

@jesse65 Great info and analysis and you leave me with a question I never considered.
If protons, by their nature, omit the EXIT release of energy, what about the ENTRANCE release? ie: those protons that released maximum energy before reaching their target?
It seems that you might have the same issues, but just in different areas.
Phil

@jesse65
thank you for this explanation. I too go to the Mayo in Phoenix. I am currently on A/S but follow all of the treatments knowing my day may come when treatment is necessary. Did they indicate in what instances proton may be better than photon? Thank you. I will say a prayer all goes well for you.

@brianjarvis
Thank you for your great information and link to that video - learned so much. Could you please write your list of questions to have for the radiation oncologist as we will be seeing on in a couple of days at Mayo.

@heavyphil A great question regarding entry doses. I never got to ask those questions because I had already decided on the Adaptive Photon Approach. I'm not sure if technology is still the same, but I read a lot about Protons leaving "tan" marks on the sides of your hips where the entry dose enters. I asked about this with my Adaptive IMRT and was told that there would be no tanning or other skin irritations because the gantry moves around you and there is not any one particular spot subjected to damaging levels of radiation (except the target area in and around the prostate). I'm not sure of the mechanics of how protons is beamed into your body or whether newer gantry technology has corrected the higher entry dose issue (my perception & words only), I didn't get that far.

To me, any irritation or tanning indicates exposure to healthy cells: the opposite of my personal treatment goals. Similar to diarrhea from photon radiation, which to me indicates unwanted exposure to the rectum. To better protect my rectum I chose to use a Bioprotect spacer rather than SpaceOar or other gel. Recently approved, Bioprotect is a saline filled balloon that provides an additional 2-3 mm space over and above SpaceOar. I am now 18 days into my 28 day IMRT and have had zero rectal side effects. None.

Also relatively newly approved and studied, Adaptive Photon Therapy constantly monitors my prostate position as the treatment is being given. Most days the Linac stops as sudden internal gas might appear and until it dissipates, a few seconds. Or it stops so the rad techs can re-position me a millimeter or two as my bladder continues to fill while laying on the table during treatment and shifts the target field slightly. This gives me comfort that the treatment dose is going where it needs to be with minimal unnecessary exposure to normal cells.

For me, I am super pleased that my research and treatment goals have led me to the right treatment for me.

@bobgolf The explanation as I understand it is that different organs have different tolerances to radiation. Some tissue can withstand large doses, while others will readily be killed. My understanding is that Protons are good for cancers within or in front of highly sensitive organs. It is used in childhood cancers where every cell in the body is vulnerable and protons can be limited to depth and reduce exposure to tissue behind the treatment area. It's used in Brest Cancer treatment to minimized radiation exposure to the heart below the breastbone. For Prostate Cancer, it depends on where the cells are located, has it moved into the prostate bed, has it metastasized to other critical areas

For me, I'm lucky to have caught my Pc early and it is totally contained in my prostate. In my situation, particularly where my lesion is located, Protons was not the best solution. No exit dose is an important feature, but not the only consideration in choosing a treatment. It falls on your own treatment goals. Mine was to preserve my long-term QOL, 10-20 years from now, and considering all risk factors and after much research, I felt that other treatments supported my goals better.

@jesse65 What you’ll find is that proton - as this graphic shows - is less likely than photons (x-rays) to cause skin irritation/tanning/burn/damage because proton doesn’t release the majority of its energy until it reaches a pre-determined depth. (This is called its Bragg-Peak characteristic.). Because of this, its initial energy at the skin can be lowered.

This has nothing to do with newer gantry technology; it’s a physical nature of protons that photons do not have.

This was a scientific discovery ( by William Bragg) when shooting protons through various substances, long before protons started being used for medical treatments.

Also, that adaptive technology you mention was first used with photon treatments well before it was incorporated into proton treatments. Each advancement builds on the previous one.

It’s great that your treatments are going well.