Texas Center For Proton Therapy Commissions Its Beam, Names Chief Physicist

The first proton therapy center in North Texas has begun testing the equipment.

One Friday last month, a group of about a half dozen physicists and physicist assistants crowded into a room of the Texas Center for Proton Therapy, eyes glued to a computer screen. To its left was a live feed of the treatment room; a glass cube filled with 50 cubic meters of water that the physicists were preparing to shoot a beam of radiation into.

Inside the vat of water was a sensor that moved upward half a millimeter at a time, testing the radiation in the water. The beam, invisible to the naked eye, is shot into the vat. The sensor moves up, up, up. Finally, the physicists get what they came for: A chart shows a line curve upward and peak before plummeting down to 0. That was where the radiation was and nowhere else, exactly what the experts wanted.

“We’re doing a small series of physics experiments literally dozens, if not hundreds, of times because we’re checking very different energies,” says Dr. Andrew K. Lee, the center’s medical director. “We’re checking different field sizes and we’re checking the beam at different angles.”

The treatment center is in Las Colinas and will be the first proton therapy provider in North Texas. The highly specialized form of cancer therapy uses a proton beam generated by a 220-ton machine known as a cyclotron. It travels the length of about half the football field into a treatment room, where a patient is lying. After weeks of careful imaging and planning, the physicist beams a concentrated dose of the radiation directly into the tumor, limiting exposure to healthy tissue. This is what Dr. Chang Chang, the director of physicists, and his team were testing, that the radiation would go where they want it to go and nowhere else.

“After a certain depth, you will see the reading becomes zero, just no dose at all,” Chang says. “It’s very, very amazing when you compare that with photon. If you look at photon, wherever you go, however deep you are, you’re going to get a dose.”

He’s talking about traditional radiation, which uses a photon to wage war on the cancerous tumor. But it’s not as precise as proton, meaning healthy bodily tissue is more likely to be exposed. This leads to further side effects and an increased chance in developing secondary cancer, as evidenced by a 2014 study in the Journal of Radiation Oncology. 

Chang says each of the three treatments room will undergo hundreds of tests before they are sufficiently calibrated. Last month, the beam had a variation of less than .1 percent in each of the 10 tests, Chang says.

That first experiment finished in less than 7 hours; in Chang’s experience, it’s been up to 16 hours. He was brought on board this summer, coming to Texas from the ProCure Proton Therapy Center in Somerset, New Jersey, where he was the senior medical physicist, involved in commissioning ultra-precise pencil beam scanning. The Texas Center for Proton Therapy is the only facility in Texas that will combine that with cone beamed computed tomography, which will provide a three dimensional view of the patient for even more precise treatment.

Currently, Chang has four physicists including himself, a number that could balloon up to seven depending on volume. Each has earned a PhD and has between three and seven years experience with proton therapy. The center has already begun providing imaging services to patients and is aiming to be treating patients by the year’s end. Chang says the team is ahead of schedule.

“Combined in this whole center we have 70 years of experience, for my physicists, it varies from three to seven years each,” Chang says. “Coming with this much experience in proton is really quite impressive in my mind. “