this past saturday, marty and i went on tours of the cyclotron (iucf) and the adjoining proton therapy facility (mpri). tours were being given as part of the physics open house taking place at swain hall (the physics lecture building on campus). this tour was amazing for two reasons: we got to see the rooms where proton therapy is administered, and we entered the main cyclotron room as well as the smaller injector cyclotron. all of this was possible because the beam was not running at this time.
first we visited the control room, which is comparable to the control room at cdf, but the equipment is much older. the folks at iucf have proudly hung many nasa banners above the consoles because iucf tests the durability of nasa equipment against radiation (in space, you no longer have the protection of the earth’s atmosphere from many forms of radiation from the sun).
next we entered the proton therapy facility, and it felt like entering a different world. the interior design of mpri is very warm and modern and has every look of a professional medical facility. this is in stark contrast to the rest of iucf’s lower level, which has exposed concrete walls, i-beams, miscellaneous equipment lying around, maze-like doors and hallways, and copious yellow signs reading “RADIATION AREA”.
first a word about proton therapy vs. x-ray therapy. traditional x-ray therapy consists of high energy photons. the photons pass completely through the patient’s body, depositing energy as they go. the pattern in which a beam of x-rays or protons depositing energy at a given depth is shown by the Bragg peak. Unfortunately, with x-rays more energy is deposited at the surface of the skin than on the tumor itself, and a substantial amount of energy is deposited on the tissue behind the tumor as well. doctors counteract this by administering several x-ray doses of short duration from various angles, such that they converge on the tumor. however, the patient may still experience side-effects of burns to the skin or damage to internal organs. conversely, proton therapy makes use of a proton beam (protons can be isolated relatively easily by stripping the electrons from hydrogen). the protons are accelerated in a cyclotron and guided to different treatment rooms with magnets. as you can see from the Bragg peak image, protons will completely stop inside human tissue within about 20 cm, where most of their energy is deposited. so a very high, very lethal dose can be administered to the tumor itself with very little damage to the surrounding tissue (hooray!). a downfall to proton therapy is that some scattered protons will impact other materials in the treatment room, releasing neutrons. children under the age of 8 are most sensitive to the ambient neutrons and have a 3% chance of developing tumors 30-40 years later as a result.
first we were shown the fixed beam room. a clunky beam line juts out from the back wall and takes up half the room. the patient bed is attached to a robot arm, which came from a toyota factory. these robots are very powerful, so they have been reprogrammed to slowly move the patient into position (within 1 mm of precision) in front of the beam line.
then we saw the gantry. this room contains a giant track, like a hamster wheel, on which the beam line can be rotated 360 degrees. this setup is several times more expensive to install than the fixed beam line, but allows one to treat tumors that the fixed beam cannot reach. the patient bed is again attached to a robot arm, as is some of the x-ray equipment. x-rays are used only for positioning a patient prior to treatment.
at the end of the tour i was very impressed, and i can see how this line of work would be very rewarding for scientists and medical personnel. proton therapy is quite painless and brings almost no side effects, since living tissue is hardly damaged. the folks at mpri are working on a way to eliminate the scattered protons to make the procedure even safer for children (though i think it’s already safer than chemotherapy or x-ray therapy). unfortunately there are only a handful of proton therapy facilities in the country, and each one is different, because the technology of a cyclotron is so unique and expensive. whereas every doctor and dentist office in the country has an x-ray machine, so that technology has been standardized for the past 20 years. a company called ProCure was started by former iucf director John Cameron, and their goal is to standardize proton therapy facilities to make them less expensive to build and optimized to treat most patients. so i’m hoping that this form of treatment becomes more standard in coming years.
