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@jesse65 Great info and analysis and you leave me with a question I never considered.
If protons, by their nature, omit the EXIT release of energy, what about the ENTRANCE release? ie: those protons that released maximum energy before reaching their target?
It seems that you might have the same issues, but just in different areas.
Phil
Replies to "@jesse65 Great info and analysis and you leave me with a question I never considered. If..."
@heavyphil A great question regarding entry doses. I never got to ask those questions because I had already decided on the Adaptive Photon Approach. I'm not sure if technology is still the same, but I read a lot about Protons leaving "tan" marks on the sides of your hips where the entry dose enters. I asked about this with my Adaptive IMRT and was told that there would be no tanning or other skin irritations because the gantry moves around you and there is not any one particular spot subjected to damaging levels of radiation (except the target area in and around the prostate). I'm not sure of the mechanics of how protons is beamed into your body or whether newer gantry technology has corrected the higher entry dose issue (my perception & words only), I didn't get that far.
To me, any irritation or tanning indicates exposure to healthy cells: the opposite of my personal treatment goals. Similar to diarrhea from photon radiation, which to me indicates unwanted exposure to the rectum. To better protect my rectum I chose to use a Bioprotect spacer rather than SpaceOar or other gel. Recently approved, Bioprotect is a saline filled balloon that provides an additional 2-3 mm space over and above SpaceOar. I am now 18 days into my 28 day IMRT and have had zero rectal side effects. None.
Also relatively newly approved and studied, Adaptive Photon Therapy constantly monitors my prostate position as the treatment is being given. Most days the Linac stops as sudden internal gas might appear and until it dissipates, a few seconds. Or it stops so the rad techs can re-position me a millimeter or two as my bladder continues to fill while laying on the table during treatment and shifts the target field slightly. This gives me comfort that the treatment dose is going where it needs to be with minimal unnecessary exposure to normal cells.
For me, I am super pleased that my research and treatment goals have led me to the right treatment for me.
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Protons do not emit maximum energy before reaching the target, This is the Bragg-Peak characteristic of protons. As the protons slow, then they begin to release energy.
Protons emit maximum energy at a certain depth. That can be calculated, and must be done exactly right (otherwise yes, the maximum energy might be released before or beyond the target).
In fact, for protons to work for radiation treatments, they have to utilize a (modified) Spread Out Bragg-Peak (SOBP) to hit the entire prostate. (See attached graphic.)