Photons vs. Protons in Radiotherapy - Why photons?

[Mirin]

Something has been bugging me ever since I learned about Bragg's peak (and how it compares to x-ray attenuation) a few years ago...

I understand there are probably advantages that photon therapy has over proton therapy, but what are they? Cost? Feasibility?

Probably a dumb question, but thanks in advance

 

[Ryan_m_b]

There's more to it than Bragg's Peak. Taken from the wiki page on Proton therapy: Comparisons with other treatments;

X-ray therapy may be described as having more "skin sparing potential" than proton therapy: x-ray radiation at the skin and at very small depths is lower than for proton therapy. One study estimates that passively scattered proton fields have a slightly higher entrance dose at the skin (~75%) compared to therapeutic megavoltage (MeV) photon beams (~60%). X-ray radiation dose falls off gradually, while tissues deeper in the body than the tumor receive essentially no radiation during proton therapy. Thus, x-ray therapy causes less damage to the skin and surface tissues, and proton therapy causes less damage to tissues beyond the target.

 

[Mirin]

Interesting, I didn't consider scatter effects. Thanks for the reply. I guess I could have found the info easily enough had I Googled a little more intelligently :p

 

[Ryan_m_b]

Interesting, I didn't consider scatter effects. Thanks for the reply. I guess I could have found the info easily enough had I Googled a little more intelligently :p

No worries, I don't mind having to read up on something myself when it's interesting.

 

[EricVT]

Cost is definitely a factor. Most radiotherapy is given in community hospitals and cancer centers. Dropping 150-200 million dollars on the equipment required for proton radiotherapy and a place to keep/use it is just unrealistic and way out of reach for those sorts of places in almost all cases. You can buy a pair of photon/electron-producing linear accelerators and shield a couple of rooms for their use for less than 10% of that.

 

[enkiddu]

Cost is definitely a factor. Most radiotherapy is given in community hospitals and cancer centers. Dropping 150-200 million dollars on the equipment required for proton radiotherapy and a place to keep/use it is just unrealistic and way out of reach for those sorts of places in almost all cases. You can buy a pair of photon/electron-producing linear accelerators and shield a couple of rooms for their use for less than 10% of that.

^^^^^ This

Also, I don't think there have been enough proton cases to be sure of all the effects. Physically speaking, they do have their advantages. Radiobiologically, higher LET radiation (like protons) have their advantages and disadvantages as well. The LINAC is still versatile and can treat in various modalities (electrons for superficial tumors, total body and total skin irradiations)

 

[ThinkToday]

Protons have some excellent applications (some Pedi brain tumors, for example), but they also have some real issues. Cost was mentioned, but with the crashing sound of bank vaults closing the price to install has tumbled in a huge way. The 2010 ASTRO was driving nails in the proton coffin. Based on the "new" concept of "evidence based medicine", the justification for broad use of protons just isn't there. The very benefit of proton depth vs. dose control is also its weakness. With protons a shift of a few millimeters can mean the difference between delivering 100% and 10%, whereas with photons it could be 100% dropping to 90%. Targets in phantoms can be treated well, target structures and organs in live people move, people move, etc., E.g. the chance to have a geometric miss goes way up with protons.

Do proton centers need to exist? Probably yes. There are applications where they are clearly superior. However, the cost of treatment, cost of installation, technical staff, professional staff, etc., should have them located regionally, and probably subsidized. Yes, subsidized, since the clinical uses would be limited and the costs are high. Additionally, there would likely be significant further research that may one day improve the indications for its use.