AVM Survivors Network

Photons vs Protons, What´s the difference?

Stereotactic Radiation; GammaKnife, CyberKnife vs Particle therapy; ProtonBeam.
What´s the difference?

This is intended as information, an attempt to describe in a simple way, and to differentiate between the various forms of radiations; x-ray/gamma/electrons vs proton/carbon and not to describe radiotherapy in details!

Each AVM is special and unique and which method of treatment that is best suited will depend on the individual patient.
Treatment options may be surgery, embolization or/and radiation or a combination of these. It will depend on different factors such as AVM size, location, feeding arteries, associated aneurysms, venous drainage and sometimes age, as well as what type of radiation treatment that is available in your area.

The concept of radiation is based on a targeted irradiation of the AVM such that cells of vessel wall damage. Vessel wall swell up and this may eventually lead to the closure of the malformation.

What is Stereotactic Radiation?
Stereotactic treatments can be confusing because many hospitals call the treatments by the name of the manufacturer rather than calling it SRS and SBRT.
Brand names for stereotactic radiation treatments include Axesse, Cyberknife, Gamma Knife, IMRT, Linac, Novalis, Primatom, Synergy, X-Knife, TomoTherapy and Trilogy...
This list changes as equipment manufacturers continue to develop new, specialized technologies to treat cancers/AVM.

Stereotactic radiation is using photons, which is X-ray/gamma and electrons
and is a specialized type of external beam radiation therapy. It uses focused radiation beams targeting a well-defined AVM, using extremely detailed imaging scans.
There are two types of stereotactic radiation. Stereotactic radiosurgery (SRS) is when doctors use a single or several stereotactic radiation treatments of the brain or spine. Stereotactic body radiation therapy (SBRT) refers to one or several stereotactic radiation treatments with the body, such as the lungs.

The most common forms of sterostatic radiotherapy are gamma knife (GK), linear accelerator (LINAC) and Cyber Knife (CK).
While the Gamma Knife is based on many sources of radiation that hits in a defined area, Cyber Knife is based on a radiation source that is placed on a robot arm and the radiation doses shot from many different angles to achieve a similar effect. There are lots of different varieties on the marked.

In stereotactic radiation therapy the radiation pass through the body/head, but the treatment is given with extreme accuracy, the maximum effect (high-dose radiation) being at the defined area/central point of all the sources, which should limit the effect of the radiation on healthy tissues (low-dose radiation). One problem with stereotactic treatments is that they are only suitable for certain small tumors/AVM. Gamma Knife can therefore usually only be used on small AVM < 3cm in diameter for best effect and obliteration, but sometimes fraction-radiation is done, e.g in larger AVM´s with only one or few feeders in the same area.

What is Proton Therapy?
In particle therapy (Proton therapy), energetic ionizing particles; protons or carbon ions, are directed at the target (AVM).

Proton beam therapy utilizes protons (charged particles found in the nucleus of an atom) compared to radiotherapy uses x-ray beams.

Physicists separate positively charged protons from hydrogen atoms by stripping off the negatively charged electrons. A machine called cyclotron or a synchrotron generate and accelerate protons. The protons leave the machine and are steered by magnets toward the tumor/AVM. Other pieces of equipment are used to modify the range of the protons, shape of the beam and to compensate for organ location.

The dose increases while the particle penetrates the tissue, up to a maximum (the Bragg peak) that occurs near the end of the particle's range, and it then drops to (almost) zero. The advantage of this energy deposition profile is that less energy is deposited into the healthy tissue surrounding the target tissue.
The unique aspect of proton beams is that they have a defined scope that can be calculated to the millimeter and can radiate very close to sensitive vital locations. Proton therapy can therefore be used for AVM near sensitive eloquent cortical regions on small and larger malformations/tumors

ProtonBeam an option when Gamma or CyberKnife can not be used?
Conventional stereostactic radiotherapy (X-rays and electron rays) can not avoid that also other tissues than the AVM receives a low-dose of radiation, because radiation pass through the body/head. Which means that even healthy tissue is affected to some degree. Often that is not a problem because is only low doses of radiation. In other cases it may be the reason that the AVM can not be treated with this type of radiation. This is because sufficiently high dose of radiation from conventional stereostactic radiotherapy can not be given to large AVM´s without a significant risk of permanent injuries to healthy sensitive tissues in eloquent brain areas.

Protons interact in a completely different way with the matter than traditional radiation. The energy of a proton beam can be varied so that the radiation dose almost completely lands on a predetermined depth. Therefore, the radiation can be almost entirely concentrated in the AVM with proton therapy, which means that the radiation dose can be increased with much less risk of side effects.
Proton therapy can be an option for most AVM, but is especially considered for patients that is not a candidate to stereostatic radiation and whose AVM´s is close to critical vital areas or with multiple feeders. Furthermore, proton therapy particularly appropriate for children, as traditional radiation provides a degree of risk for tumors later in life.

Again, this is just an attempt to simplify the difference between photons and protons, because I have the impression that there is a lot of confusion around this issue. After writing all this, I do not know if I actually managed the task? lol
Gamma Knife Complications?
AVM of right temporal lobe. Looking for right treatment

Hanne, Are you kidding me? You managed the task very well. This is a much needed post to help eliminate confusion on all this radiation stuff. It is confusing and there are options that each AVMer should understand to make an informed decision.

I’m no expert on Proton-beams because it was never expressed to me at the time as an option by the 4 Neurosurgeons I interviewed, however one of them said out of the blue that he would not recommend it. Why he said that? I have know idea, I never thought much about it afterwards, but the way you explain it, it sounds like it could be a good option for some.


Thank you Brett :slight_smile:

I agree, there is a lot of confusion around this topic and I also have the impression that neurosurgeons have different views regarding proton vs photon treatment.

The reason I started to do some research on my own was because I was told there was no treatment options at all for my AVM and also because I have had questions about this subject from other avmsurviors.

The reason I am not a candidate for stereotactic radiation (X-rays; gamma knife, cyber knife) is due to the fact that my AVM is too large, with too many feeders in a very eloquent area (motor/sensory).

This is the explanation I got from the neuroradiologist: "They can not do fractionated stereotactic radiation because there are so many feeders to different parts of my AVM that even if they managed to block some of them they would not manage to block them all in one session and therefore my avm will continue as before.

If they were going to radiate the whole AVM in one session, the radiation would be too high and I was told that I would become 100% permanently paralyzed because there would always be some radiation adjacent to the AVM and healthy functional tissue would be damaged. They referred to previous experience with similar AVM as mine, they simply refuse to do it."

That is the overall reason why they can not treat large AVM with stereotactic radiation (x-rays), there will always be some low-dose radiation as well but in small AVM´s the dose is more tolerable.

Since my AVM can not be operated on by surgery or embo I was told that nothing could be done at all.

Anyway, the neurosurgeon have now sent my pictures to a hospital in Sweden where they do Proton treatment. That made me curious, what is the difference?

Today I understand that we are talking about two totally different types of radiation and technics. If I am actually a candidate for Proton treatment I do not know yet, but will soon get an answer, finger crossed…

So, there may still be a hope for treatment, but if the AVM will be obliterated after being beamed with Proton, only time will tell.


HAMIDAH: I am glad you found the information on photon radiation vs proton beam useful.
It has been very clarifying for me as well, writing it.
Having said that, remember each AVM is unique and special and that the neurosurgeon will know which type of radiation that fits best for your son.

Hanne xxx


I am thinking of going for the novalis protocol. Which one of the above is novalis?


Kyle said:
I am thinking of going for the novalis protocol. Which one of the above is novalis?

Kyle: Novalis is stereotactic radiation

Hanne xxx


Robin Konen said:

I just read your explanation of various treatment options. It was very good. When I first started treatment, I was told I would have a series of embolizations followed by gamma.
After the last embo, they said I would get LINAC. No one could explain the difference to me. Thank you so much for your research and for sharing with us.

Robin: When my neurosurgeon mentioned that I might be a candidate for radiation, either gamma or proton, I asked him what is the difference and he could not explain it either.

Knowing the difference today, make me wonder why not?

Since I have a very large AVM I would have wanted to know the pros and cons for both methods before I got the frame on!

Hanne xxx


Thank you so much for explaining all of the options available to us. I really appreciate hearing all the different options, and you enlightened me on alot of knowledge. I will keep you in my thoughts and prayers that the proton therapy is an option for you. take care.


Thank you Diane :slight_smile:

When it comes to the effect of Proton beam therapy. I will give updates as time progress.
That is, IF I am a candidate for the treatment…
Hanne xxx


Just after my gamma knife treatment, I was watching the Science Channel on TV where they were describing what happens when a star explodes, and becomes a super nova. They said it primarily emitted deadly gamma rays!!! That got me to thinking!!!

Dewdo from the other Washington


Thanks for all the information. I appreciate it. I’m so lost and was never told about the different types of radiation so I’m clueless. Worse part is I have no say so in this. He is in the county jail for doing something stupid but hasn’t been charged yet except to say his is compendent and will await his medical treatment before proceeding with his case. He was scheduled for surgery in September 2010 but the jail didn’t get him there. So now it’s grown more and they aren’t sure they can do surgery at all, I feel so helpless.


Latest Update on my Proton Treatment:

Dr Chapman and Dr Loeffler at MGH has reviewed my images in detail and concluded that it will be feasible to treat me under GA. (8 Mars 2013)
...and that they will be pleased to begin organizing my visit as soon as they get it confirmed from the National Hospital in Norway.

Problem was, that this letter never found its way to Norway but Sweden.
That said, I have informed Dr Berg-Johnson about this letter now (3 June 2013) and he sent a renewal of my financial guarantee from the state.

All I can do now is to wait for him to get back from his summer vacation. Also I need the Hospital in Norway to find two nurses to travel with me in case I need acute medication due to my seizures...

So, still waiting, after more than 3 years (!!) for an answer if Proton treatment is a choice for me..

I will keep update when I know more about when or if the Proton treatment actually will happen (?) and the effect it might have on my AVM, as time progress.


I have never forgotten how you welcomed me here to this site! You are always in my thoughts and prayers!


Hanne, I pray ever day that your country will provide you with the support you need. Keep the Faith, Dear Hanne!

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