Radiation Margins CT vs MRI guided radiotherapy v proton

Dr. Brian Davis has a lot of experience at Mayo Rochester treating patients with protons. He discusses what he calls the "hype" around proton therapy in a video presentation entitled "Proton Therapy for Prostate Cancer"

Dr. Mack Roach, in a presentation discussing a few different aspects of radiation therapy for prostate cancer, discussed problems he sees with the leading study of MRI-Linac around minute 15 in a video entitled "Radiation & Side Effects For Prostate Cancer | Mack Roach III, MD & Q+A with Mark Moyad, MD"

@jeffmarc
You're always helping us out online. Take care of yourself now! Hoping for a swift recovery and good results.

@climateguy
Thanks! - listened to the first video, Dr. Brian Davis from Mayo Rochester . About the 14 minute mark he says "“we rarely treat post-prostatectomy patients with proton - we like the rapid cone beam CT to see the bladder and rectal placement and repositioning the beam as necessary.... but if we want in 2027 with new proton center we can do more of it. “
My head is spinning! - so at Mayo Rochester they don't use MR Linac OR proton for post-RP radiation - do you know, is the cone beam CT the delivery method or the imaging method?

@jeffmarc Good luck, Jeff!

@climateguy Interesting how proton radiation is considered generally superior for other solid tumor cancers located near critical, sensitive structures due to its precise targeting and reduced entry, scatter, and exit dose, leading to fewer side effects, but (for some reason) not so for prostate cancer.

Hopefully, the same laws of physics still apply to prostate cancer; does patient compliance play a role as well?

@brianjarvis The promoters of protons point out the theoretical advantages. The doubters point to what has been observed so far in the results. It isn't a brand new technology - Loma Linda has been treating with protons since 1990.

A proton facility has been so expensive for an institution to install that there is an incentive for the bean counters in the back rooms to want to promote maximum use, to justify the expense.

Eg.: in the city where I live the NCI designated cancer center has protons. They heavily advertise them for prostate cancer, especially on regional sports broadcasts. I was a bit astonished when I asked my RO at this facility about protons. He said the prostate cancer group there did not favor protons for prostate cancer. They thought the ads were misleading.

The results have been superior for other cancers.

@klein505 The cone beam CT is an improved imaging system. Compared to a standard cat scan, the cone beam CT exposes patients to far less radiation, producing an image with way more detail, and faster.

I'm in the middle of a 20 session treatment regime where the machine uses cone beam CT imaging. Each of my sessions is very short. The setup takes a few minutes. When they start the treatment, the beam is on intermittently, and for only a few minutes.

Your mileage may vary. I haven't had a prostatectomy. My treatment is aimed at my cT3b case. They've done HDR brachytherapy a few weeks ago, and now this. As far as I know they are aiming to treat the whole prostate and a margin, plus some pelvic lymph nodes. I've been on ADT for 6 months already.

I was astonished at how short these external beam treatments are. They are using what they say is their new machine - a Varian Ethos that they say is faster than all the others they have.

I will add this commentary on Proton without a spacer, while this might be an older piece of research there seems to be some similar articles out there. I agree with others I would not worry about it just yet but this topic should be researched before I would schedule any treatment.

@climateguy Actually, they’ve been using proton radiation for prostate cancer since at least 1979. When I was researching this back in 2020 (leading up to my treatments during April-May 2021), the earliest reference to protons being used for prostate cancer treatments that I could find was a 1979 JAMA paper titled “Proton radiation as boost therapy for localized prostatic carcinoma” https://pubmed.ncbi.nlm.nih.gov/107338/

We need to remember that application of proton radiation wasn’t discovered in the medical community; it was discovered in the scientific/physics community; it was there they discovered that these heavy subatomic particles with wavelike properties acted differently than photons (x-rays).

It was the physicist William Bragg who discovered that protons deposit most of their energy right before coming to a stop, which is key to modern proton therapy for treating cancers - they can pre-determine where exactly the proton releases its energy.

So, this is not a “theoretical” advantage. This “Bragg-Peak characteristic” (as it’s called) is a scientifically proven advantage over photons in the scientific community that later, someone said “Hey, maybe we can apply this in treating solid tumor cancers in order to reduce the entry-dose, scatter, and exit-dose that is inherent with photon radiation?”

Proton radiation has since been used to successfully treat many types of cancers: pediatric, head, neck, lung, brain, breast, esophageal, pancreatic, liver, rectal, eye, cervical,…..and various types of recurrent cancers. So beancounters notwithstanding, there is less of a need to mis-represent in order to justify the expense.

Despite the cost, three more proton centers have come online in the U.S. just this year (https://www.proton-therapy.org/map/).

I think they promote them on regional sports broadcasts because that’s where the audience is. (Advertising it during “Dora the Explorer” probably wouldn’t be the best use of resources.)

I have read in a number of places that proton radiation is considered generally superior for other solid tumor cancers. So, one must wonder “Why not for prostate cancer?”
> are the laws of physics different?
> is prostate cancer tissue different?
> do the treatment centers all not do the calculations the same? (That has happened by the way.)
> is patient compliance an uncontrolled variable in these studies?
> ????

So, I go back to the science. (As a retired computer scientist who eats, lives, and breathes data, I’m not prepared to accept the statement “The results have been generally superior for other cancers…just not for prostate cancer.”) There has to be justifiable rationale for that.

What I considered —> What does science say protons should do when entering a substance? They will always deposit most of their energy right before coming to a stop. It generally works for other solid tumor cancers; I was convinced (as much as one can be) that it had to work for my prostate cancer.

As a patient, my job was to do everything exactly right so as not to introduce an uncontrolled variable into the treatment equation. If everyone on the team (including me) did their job exactly right, protons for my cancer treatment should work exactly as it would when firing these same heavy particles into material in a science lab.

(As one who likes to drill down into the gory details, I would’ve asked those ROs what specifically about those ads were misleading and why they did not favor protons for prostate cancer. I do that when the forum is appropriate, and the responses are usually a bit more nuanced.)