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Radiation Margins CT vs MRI guided radiotherapy v proton
My husband is 2 1/2 months post RP, which went really well. Our first PSA test post-RP is due soon.
Just in case, we are trying to understand treatment options if radiation is on the table. At first we thought proton - but reading about CT guided vs MRI guided photon treatments, it looks like MR-linac is a clear winner when it comes to reducing side affects. The treatment margins are half of CT guided radiation: 2 mm compared to 4 mm. That 2mm difference might mean a much lower dose of radiation to the at-risk organs.
https://www.urologytimes.com/view/mirage-trial-margin-reduction-with-mri-guided-sbrt-reduces-toxicity-vs-ct-guided-sbrt
Especially since you can't use spacer OAR gel type buffers to protect the colon once the prostate has been removed. (I think that's right)
I'm not sure about the proton beam margin advantages..
Has anyone anything to share? Our treatment facility doesn't appear to have a MR-linac or similar system. Is it worth looking for one that does?
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If I read that article correctly, they were comparing MRI-guided SBRT (photon) vs CT-guided SBRT (photon); neither were proton.
The MRI-guided is IGRT, which has advantages over CT-guided. That’s probably why there’s less toxicity.
Using a rectal spacer to shield the rectum from salvage radiation post-prostatectomy is rarely done. Here’s one case when it was done successfully: https://pubmed.ncbi.nlm.nih.gov/25339311/
Proton has 2mm margins as well. The value of proton is its Bragg-Peak characteristic. (See attached graphic.) The heavy particle (proton) has little entry-dose, scatter, or exit-dose. When it hits a target at a calculated depth, it releases all of its energy right there; none passes through to (possibly) hit nearby organs and tissues (as happens with photons).
You may go a decade or more before he needs salvage radiation. By then they may have completely new techniques. It’s a little early to start planning. Around 60% of RP patients never need salvage radiation.