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Protons are different than Photons

choclabs
Posts: 23
Joined: Feb 2016

Let us all agree that less body tissue which becomes radiated is better than more body tissue that is radiated while under therapy for PCa.

Then we must also agree to understand that Protons when used as the source of radiation are unlike Photons. The radiation energy in photons (X-Rays, Gamma rays etc) is present in the beam prior to the tumor site and exiting the tumor site.

The below quote is from Wikipedia. https://en.wikipedia.org/wiki/Proton_therapy

"Due to their relatively large mass, protons have little lateral side scatter in the tissue; the beam does not broaden much, stays focused on the tumor shape and delivers only low-dose side-effects to surrounding tissue. All protons of a given energy have a certain range; very few protons penetrate beyond that distance.[4] Furthermore, the dose delivered to tissue is maximum just over the last few millimeters of the particle’s range; this maximum is called the Bragg peak often referred to as the SOBP.[5]"

"To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy, typically given in eV or electron volts. Proton therapy treats tumors closer to the surface of the body with lower energy protons. Accelerators used for proton therapy typically produce protons with energies in the range of 70 to 250 MeV (mega electron volts; million electron volts). Adjusting proton energy during the treatment maximizes the cell damage the proton beam causes within the tumor. Tissue closer to the surface of the body than the tumor receives reduced radiation, and therefore reduced damage. Tissues deeper in the body receive very few protons, so the dosage becomes immeasurably small.[4]"

"In most treatments, protons of different energies with Bragg peaks at different depths are applied to treat the entire tumor. These Bragg peaks are shown as thin blue lines in the figure to the right. The total radiation dosage of the protons is called the spread-out Bragg peak (SOBP), shown as a heavy dashed blue line in figure to the right. It is important to understand that, while tissues behind or deeper than the tumor receive no radiation from proton therapy, the tissues in front of or shallower than the tumor receive radiation dosage based on the SOBP".

Precision delivery of radiation to the exact location of the tumor is also critical. Proton beam radiation therapy locations that have kept up with upgrades to their systems can absolutely deliver real time radiation placement as well as any photon based system. What I mean by real time radiation placement, is that slight movements from bowel contents passing, breathing, muscle spasm and others, while under treatment cause the prostate to move and thus the system must adjust so that during the treatment all radiation energy delivered remains focused on the tumor cells. Some therapies actually have the patient purge their bowels prior to each session.

FYI - Michael

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