IMRT and IMPT are very similar. They are both Intensity Modulated and capable of being programmed to attack the exact shape of the tumor. The "R" stands for radiation the "P" for proton.

There is a significant distinction between standard radiation treatment and proton therapy. If given in sufficient doses, conventional radiation techniques will control many cancers. But, because of the physician's inability to adequately conform the irradiation pattern to the cancer, healthy tissues may receive a similar dose and can be damaged. Consequently, a less- than-desired dose is frequently used to reduce damage to healthy tissues and avoid subsequent unacceptable side effects. The power of protons is that higher doses of radiation can be used to control cancer while significantly reducing damage to healthy tissue and vital organs.

Proton Beam Therapy, as the name implies, uses protons to fight cancer. Protons are stable, positively charged subatomic particles with a mass 1800 times that of an electron. These characteristics allow the proton's dose of radiation to be controlled to an exact shape and depth within the body.

The main difference between protons and X-rays is based on the physical properties of the beam itself. Protons are large particles with a positive charge that penetrate matter to a finite depth based on the energy of the beam. X-rays are electromagnetic waves that have no mass or charge and are able to penetrate completely through tissue while losing some energy. These physical properties have a significant bearing on the treatment of patients.

The photons or electrons used in conventional radiation therapy deposit most of their energy in the tissues they pass through before reaching the tumor and often deliver radiation beyond the targeted tumor to surrounding normal, healthy tissue. Although advanced techniques such as intensity-modulated radiation therapy can reduce the exposure of healthy tissue to radiation, with photon radiation therapy, the delivery of at least a small amount of radiation to these structures cannot be avoided.

Protons are energized to specific velocities, and these energies determine how deeply in the body the protons will deposit their maximum energy. Since proton beams are heavier than their conventional counterparts, they can be delivered more precisely and prescribed to cover the entire tumor. The result: proton beams can treat tumors deep within the body while producing minimal or no side effects in surrounding tissues.

M.D. Anderson feels good enough about it to invest 125 million in a whole new treatment center for it, scheduled to open in 2006.

If I had to do it over again, I would put this high on my list of potential treatment therapies to investigate. Over 33,000 patients have been treated with this technology since 1990 when it was introduced. Unfortunately only a few institutions are offering it at this time.

The treatment machine is over 200 tons and uses voltages as high as 250 mEV (million Electron Volts)(compared to 20mEV for a high powered LINAC) 6-12 mEV being typical for head & neck cancers. The rotating gantries are 35' in diameter and dwarf conventional LINACs which weigh in at a paltry 9 1/2 tons.

I believe that at least one member of the board was treated at LLUMC.

Long term data is still being developed for survival rates. LLUMC is preparing a 10 year study of prostate cancer patients. Like IMRT, IMPT was developed for prostate cancer and found a niche in the head & neck realm (among many others).

My personal feeling is that IMPT will eventually become the gold standard.

For those wishing further information type "proton therapy" in Google and you will access all of the articles I cited and quoted from. "IMPT" was not a very good search term.

Some of my sources were MD Anderson, Harvard University, LLUMC and Optivus. Used without permission.