5 Questions on Proton Therapy

By Patrick Hwu, M.D. - December 20, 2021

Dr. Louis Harrison, chair emeritus of the Radiation Oncology Department, is internally renowned for developing personalized radiation therapies and building an innovative program. He recently sat down with me to discuss bringing proton therapy to Moffitt Cancer Center.

Dr. Louis Harrison, chair emeritus of the Radiation Oncology Department
Dr. Louis Harrison, chair emeritus of the Radiation Oncology Department

Hwu: Today we’re going to talk about proton therapy, a really exciting modality to treat patients that gives them a unique opportunity for a great outcome. Dr. Harrison, can you please start by letting us know what proton therapy is?

Harrison: Most people are familiar with electrons, protons and neutrons. A proton is a subatomic particle that is positively charged, an electron is negatively charged and the neutron is neutral. A proton

becomes a cancer therapy when you introduce very sophisticated technology called the cyclotron. It’s a 50 ton piece of technology that takes the proton and accelerates it in larger and larger spirals to make it faster until it becomes a very high speed projectile. It organizes the protons into beams that you then direct into the body at a tumor. This is how proton therapy becomes a cancer therapy.

Hwu: How does it differ from standard radiation therapy?

Harrison: Standard radiation therapy is done with photons or X-rays. X-rays are energy packets that don’t have weight. Generally, the way photon radiation works is that you accelerate electrons along a straight path and that machinery is called the linear accelerator. The electrons hit a heavy target and it sets off X-rays that go into the body. The major difference between X-ray therapy or conventional radiation therapy and proton therapy is what happens when these beams go into the body. When an X-ray beam goes into the body, it deposits radiation along the path of the beam. Although it’s directed at a tumor and although most of the radiation goes into the tumor, the areas along the pathway of the beam going in and out do leave radiation along those paths, and so the tissues around the tumor get radiation. We’ve gotten better and better at formalizing the radiation to the tumor but the areas around the tumor get radiation.

Now imagine this is the spinal cord next to the tumor, and you want to give all the radiation to this, you want to give no radiation to the spinal cord. Proton therapy focuses all the radiation in one spot or one very specific geographic area and gives almost no radiation to the nearby organs. In those situations proton therapy offers enormous advantages.

Hwu: Tell us about the multidisciplinary approach for radiation at Moffitt Cancer Center.

Harrison: Well, this is something that we’re all very proud of. It is a very unusual situation in solid tumors and cancers nowadays that a patient only gets one treatment. There’s surgery, radiation therapy, chemotherapy and immunotherapy. And the beauty of a multidisciplinary team is for the best heads to get together around a single patient and talk about what are the best options for a patient. Moffitt has been a leader since the very beginning in understanding the multidisciplinary nature of cancer and is organized around these multidisciplinary teams so that the patient is at the center of all of this.

Hwu: Can you tell us a little bit about our plans at Moffitt Cancer Center for proton therapy?

Harrison: Yes, we’re excited to see that in 2022, we’re going to be organizing all of the key elements

to develop the Moffitt Proton Therapy Center. We’ve been fortunate to get a philanthropic gift from the Richard M. Schulze Family Foundation, and that’s going to be a very important component of us doing this. The proton center is going to be located at the McKinley campus. We are making our decisions about the exact technology, location and other aspects of program development to put us on the path to get this project going.

Hwu: Proton therapy started decades ago but it’s still evolving and there’s been some very exciting technical developments. We’re going to have the latest machinery that will allow us to do certain things that the older machines can’t do. Can you describe some of that?

Harrison: Sure, well you know the cyclotron that I spoke about was developed in the 1930s. Proton therapy really didn’t start until the 1970s, but nowadays the future is actually going to be far more exciting than where we are now. What has happened up until now is that we have exploited the physical properties of protons and the ability to put a proton directly into a tumor and not affect the surrounding tissues. That has been the mainstay of the use of protons. What’s happening now is we’re beginning to understand the biology of proton therapy, and understanding the biology allows us to exploit how a proton kills a cancer cell and how we can then modulate the use of protons to be more effective in killing cancer cells. For example, if the damage that’s done by a proton to a cancer cell is that it shreds a cell in a different way than a photon, that opens up opportunities for immunotherapy and radiation to work in special ways together because of the activation of the immune system. There’s also been a new development called flash, or the ability to accelerate these protons and deliver the entire treatment in two seconds. That’s just amazing. We have to understand the biology more and we have to study this more, but it seems to be the case that when you use these very high dose rates, the damage to the tumor remains, but the damage to the surrounding tissues goes down dramatically.

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