MRI-Guided SBRT vs Proton Therapy (5-fraction)

Ask Hopkins about the margin advantage with photon. It depends upon the machinery. If the treatment margins are lower with photon, consider it because of the near the bladder G7. My understanding is that the side scatter with proton is greater than photon which makes it a better choice than proton for the prostate. Do you have a link for the the issue of bladder protection. Thanks. I appreciate your question. Have a similiar (though worse) situation. Have decided upon viewray MRIgRT because of the margin advantage.

Thanks, Gently. I think my OR mentioned a 3mm margin with the proton (pencil beam). Not sure if he mentioned a 2mm margin with the MR-SBRT or that is something I read. Definitely something to follow up on and clarify.

Check out: http://www.tandfonline.com/doi/full/10.1080/0284186X.2021.1947523
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10526919/#B49-cancers-15-04657

@chaimkugel
I would speak to a oncologist/radiologist and get second opinions.

I am not sure the research on your comments about photon and proton. Proton beam radiation (which is what I had) is very precise. It has little or no damage from radiation going in, very precise beam. and does NOT proceed past the prostrate or where it is programmed to deliver the radiation.

Photon radiation does proceed past the prostate and outside the body thus can damage additinal tissues and organs that proton does not. I chose proton radiation and got pencil beam based on the physics department at UFPTI and my oncologist/radiologist.

Mayo Jacksonville does the SBRT with photon radiation and even though very precise the radiation does proceed past the prostrate versus proton and thus I chose proton at UFPTI. I think best suggestion would be second opinions and go over the pros and cons of each. Then do some research of your own and decide what is best for you based on the opinions you got and your own research of both treatments.

Daniel Song, MD was my Radiation Oncologist at Johns Hopkins and I definitely recommend him, and JH. They have a number of Radiation Oncologists, at both Baltimore and Wash DC locations, and friends have been treated by excellent ROs at both.
Other COEs also should be excellent choices.

The Photon vs. Proton question is one of the least well documented at this moment and something that I struggled with considerably. PCF repeatedly states generalizations about how there is no proven benefit to Proton radiation over Photon: "Protons are similar to photons (traditional x-ray radiotherapy) in many ways. However, proton beam therapy has not been shown to improve cure rates or quality-of-life outcomes over other forms of radiation therapy, and may actually increase rectal side effects." I have made several requests for a deeper dive and tried to bring up the topic on webinars, but, got a strong 'read our statement' reply.

I can see a lot of reasons for the lack of clarity including the fact that the research is indeed not done and may not even be planned. Of course, comprehensively defining the efficacy and side effects comparison is beyond layman and Drs. alike.

Additionally:
- Proton machines, that cost upwards of $150M, are not widely available, hence, publishing reports that they produce better results opens up an issue on treatment equity.
- Centers that offer proton radiation are likely biased since they have to recover the cost of investment and that won't happen if their Drs. don't insist that it's better.
- While photon side effects from 'shoot thru' radiation cause side effects, the treatment protocols have been in place for 20+ years and, for the most part, patients fully recover.

I was treated, tried-modally, with ADT/Orgovyx; 2x SBRT boost radiation @ UCSF and 25xEBRT @ Stanford (15/16 cores: 3+4; 1/16 cores: 4+3). There were many reasons for this choice and I considered the full range of available options including those with significant travel. Proximity to the treatment center is certainly an important factor and visits to Stanford are almost fun as the campus is so beautiful and the staff so pleasant. Stanford, where many of today's radiation techniques were pioneered by Dr. Malcolm Bagshaw, et al, stated, categorically, that there was no proven advantage to proton radiation, which they do not offer. It was only in a sidebar conversation with a resident that I learned that the machines were coming in 2025, but, like all building decisions in Stanford/Palo Alto, it's nearly impossible to get approval to build.

Thankfully, my treatments concluded about a month ago and most side effects are gone or are highly reduced.

Thanks SeaSuite for your thoughtful response. Glad to hear you are doing well!
Either treatment seems like a good option, so I am concerning myself with the QOL side effects and the location of my G7 right up on the capsule, next to the bladder. The MR-guided SBRT has a margin of 2mm (to Proton's 3mm) and it accounts for realtime movement and automatically gating (shuts off) if off target. Also, MR-guided SBRT's urethral-sparing techniques have demonstrated significantly low rates of acute genitourinary toxicity in trials. Additionally, while proton therapy lowers the dose at several rectal DVH points compared to photons, in turn, photons limit the high dose to the bladder slightly better than protons. And the proximity of my G7 to my bladder leaves me seriously considering the MR-guided SBRT now because of high degree of focus and control. For the reasons you mentioned, there is not clear data out there that makes proton a decisive choice, particularly with the location of my PCa.

Thanks JC, that's exactly what I am doing. I have been leaning towards Proton for the reasons you mentioned and I confirmed that my insurance will cover it before I got emotionally invested in it. Either treatment seems like a good option, so I am concerning myself with the QOL side effects and the location of my G7 right up on the capsule, next to the bladder. The MR-guided SBRT has a margin of 2mm (to Proton's 3mm) and it accounts for realtime movement and automatically gating (shuts off) if off target. Also, MR-guided SBRT's urethral-sparing techniques have demonstrated significantly low rates of acute genitourinary toxicity in trials. Additionally, while proton therapy lowers the dose at several rectal DVH points compared to photons, in turn, photons limit the high dose to the bladder slightly better than protons. And the proximity of my G7 to my bladder leaves me with a few questions (which I am pursuing).

chaimkugel: I had similar numbers to you. I looked at Proton, MRIdian narrow margin machine and removal. I went to 5 radiation oncologists, including Weill Cornell/NY Presbyterian, Miami Cancer Institute and Moffit cancer center. I decided on the Mridian using 2mm margins, real time mapping and adjustments, if needed, and 5 fractional treatments. Finished last February. I also had the spacer, Spaceoar, though BioProtect is supposedly more effective now, to add space between my rectum and the prostate and minimize exposure. Like you, QOL was important. The Mirage study compared normal 3-5 mm margins to the Mridian. If I had a biological re-occurrence, I would make the same decision again. I also had the Decipher test from my biopsy material which DOES get used by doctors to evaluate treatment.

I understood the risks and tradeoffs between the different types of photon machines, types of Proton machines, ablation (hot and cold) and removal. The Mayo clinic web site is obviously really helpful. It was also helpful to speak to patients on the phone. Some cancer centers have volunteer patients and some do not. Private message me and I will be happy to speak with you about my experiences and decision process.

Just messaged you- thanks for your response!

@chaimkugel I also closely evaluated the position of my core 16 L1 - Left Posterior Apex Peripheral Zone that was 4+3; the other 5 cores with prostatic adenocarcinoma, 3+4, were all located in adjacent zones (the remaining 10 cores showed no cancer). You can then speak to ROs who, typically, don't delve into PCa position conversations without prompting. I found it highly useful to consult with a retired urologist friend who spoke to me under 'cone of silence' in addition to several other ROs and urologists who gave formal opinions largely representative of their institutions.

As has been mentioned, the Decipher Grid is one of the best predictive tools available and a PSMA PET can provide an additional layer of reassurance. As far as future treatments, that hopefully will never be needed, I am confident that with AI driven and other advancements, what we have available in 10 years will make the current offerings 'primitive'.

Best of luck to you! It was certainly reassuring to know that I did my best to evaluate alternatives.