The Emory Proton Therapy Center will be the first center of its kind in Georgia to offer patients access to this new, state-of-the-art radiation therapy. Staffed with physicians and other medical professionals from Winship Cancer Institute and Emory Healthcare who have the necessary expertise in radiation oncology and proton therapy to operate a world-class facility.
Mark McDonald, MD, discusses Proton therapy vs Photon Therapy and the ways in which Winship’s unique position helps to lead cutting edge research and clinical trials in Proton Therapy as an advanced treatment modality.
Comparisons: Proton Therapy versus Photon Therapy
Featuring:
Dr. McDonald is the associate director of the residency program in the Department of Radiation Oncology. He is actively involved in teaching and research activities for the residency program and for rotating medical students.
In 2017, Dr. McDonald was selected to the Emory Medicine Professional Leadership Enrichment and Development Program.
Before joining Emory in 2015, Dr. McDonald worked at the Indiana University Health Proton Therapy Center, providing proton therapy primarily to patients with skull base, head and neck, and brain tumors.
Mark McDonald, MD
Mark McDonald, MD, is a board-certified radiation oncologist in the Department of Radiation Oncology at Emory University School of Medicine in Atlanta, GA. Dr. McDonald practices general radiation oncology and specializes in the treatment of head and neck, gastrointestinal and lung cancers, skull base tumors, and tumors of the brain and spine. He serves as the Medical Director of the Emory Proton Therapy Center set to open in late 2018. He has extensive experience with proton therapy, a specialized form of radiation therapy. He treats patients at Emory University Hospital Midtown.Dr. McDonald is the associate director of the residency program in the Department of Radiation Oncology. He is actively involved in teaching and research activities for the residency program and for rotating medical students.
In 2017, Dr. McDonald was selected to the Emory Medicine Professional Leadership Enrichment and Development Program.
Before joining Emory in 2015, Dr. McDonald worked at the Indiana University Health Proton Therapy Center, providing proton therapy primarily to patients with skull base, head and neck, and brain tumors.
Transcription:
Melanie Cole, MS (Host): Welcome to Emory Healthcare Rounds. I’m Melanie Cole. Today’s topic is proton therapy versus photon therapy. My guest is Dr. Mark McDonald. He’s the medical director of the Emory Proton Therapy Center. Dr. McDonald tell us a little bit about proton therapy and photon therapy and start with proton. What is it used for and what types of cancers can be treated with proton therapy?
Mark McDonald, MD (Guest): Proton therapy is a type of radiation treatment. It is different from the more commonly used x-ray-based radiation because it uses proton particles to deliver the radiation. The main way that it’s different is that it’s better able to concentrate the radiation in the target and reduce and sometimes eliminate unnecessary radiation to things that aren’t supposed to be receiving it. Both types of radiation are commonly used to treat cancers and some noncancerous tumors, and they're actually both very integral to the practice. I think it’s a false dichotomy to say that it’s proton versus photon. Both types of radiation are very useful in certain circumstances. Our goal as clinicians is always to bring the best treatment to the patient.
It can vary depending on the situation and what we’re trying to treat. Proton therapy is generally used in treatment of curative situations. It’s often used in the treatment of brain tumors, head and neck tumors, many childhood cancers, lung tumors, gastrointestinal tumors. It can be used in a wide array of situations. Again, when we are selecting proton therapy, it’s because we believe there may be a clinical benefit to the patient when we use that technology.
Melanie: Then speak about how the applications of both are different. You mentioned some of the cancers that proton therapy would work for. Tell us a little bit why. What is the application that you would see a need for picking one over the other?
Dr. McDonald: I think brain tumors make a very good explanation of the advantages of the proton therapy. When we treat brain tumors with x-ray therapy, the beam comes in, it treats the tumor, and it continues beyond. Exposing normal brain on the way in and beyond the target to higher doses of radiation than we see with proton therapy. With proton therapy, the radiation comes in and the maximum energy is deposited at the location of the tumor. At which point, the protons stop with no radiation to the brain beyond the tumor.
When we think about tumors that we commonly treat in the brain—meningiomas, pituitary adenomas, schwannomas—a whole variety of non-cancerous tumors where the patient has a long, normal life expectancy, radiation is very effective in the treatment of these tumors. It can have downstream consequences that can show up months, years, decades later. These can be reduced or avoided with proton therapy by reducing the amount of normal brain tissues that’s unnecessarily exposed to radiation. So, it’s certainly a preferred radiation treatment option for many tumors that are in the brain where patients have a good chance of cure and are at risk for long term side effects of radiation.
Melanie: You mentioned the down stream exit dose. Explain a little bit how proton therapy is a little more sensitive to tissue density than photon therapy; and how it would affect tumors at a greater depth. Are the physics of photons what make it a little bit difficult to avoid that exit dose downstream from the target?
Dr. McDonald: The way that protons are different is related to the physical interaction in the body. So, x-rays behave one way and protons behave a different way. The physics to proton therapy, the characteristic is termed the Bragg peak. That refers to the maximum energy being deposited at the depth of the tumor followed by an abrupt drop off in the radiation. So, a sudden rise then an abrupt drop off looking like a peak when you graph it out. This Bragg peak means that the proton therapy stops in the body. After reaching the depth of the target, the radiation stops, not exposing tissues beyond that point to unnecessary radiation.
It is true that proton therapy, like x-ray therapy or photon therapy, is sensitive to many different characteristics of the patient including tissue heterogeneities. So many things are taken into account during the treatment planning process to develop the most accurate treatment plan. All plans have uncertainties. No radiation plan is perfect. In many cases, proton therapy can help us to reduce and sometimes eliminate radiation to things that aren’t supposed to be receiving it. We don’t see radiation toxicities in areas that don’t receive radiation.
Melanie: Where does organ motion play a role in your decision of which radiation treatment to use? Alternation and bone position or lung expansion. Can that effect the target coverage and dose to the surrounding structures, which is what you're saying you're trying to avoid.
Dr. McDonald: Absolutely. So, organ motion is an important parameter applicable in all types of radiation. We need to account for the fact that many times the target is moving. This is particularly true when we’re treating a target in the lung or in the abdomen. These areas tend to move with breathing. We have a number of ways to account for that. With photon therapy, breathing is often less of an issue than with proton therapy. It can be more sensitive. Fortunately, a number of software tools and technical interfaces have allowed us to improve our ability to account for organ motion during respiratory activity.
So, with proton therapy, we can account for this with a variety of planning techniques and a variety of patient techniques, such as breath hold. This allows for the delivery of a proton therapy to a small treatment volume while accounting for the fact that the tumor can move some during the breathing cycle.
Melanie: Speak a little bit about patient selection criteria for this decision. Is informed consent a significant issue? Then also speak about the expense. Does that play a role in this picture? Is proton more highly labor intensive with higher operational costs? Speak about that and how you might adjust that if you're dealing with patients such as children.
Dr. McDonald: So, when we talk about radiation therapy, it always starts with a consultation. Part of the consultation is reviewing the patient’s history. Performing a physical exam, reviewing the images that a patient has done. Then explaining the radiation options and determining the best plan of care in terms of radiation with the patient. Proton therapy is not always the most appropriate option. So, when we select proton therapy, it’s because we believe that there's going to be a clinical benefit.
How do we know then? It’s based on past data that’s been acquired where we understand that a certain dose to a certain structure results in a certain risk of toxicity. We know from past data and models that if we can lower the dose by a certain percentage then we can reduce that risk or, in some cases, eliminate a risk. We’re not always able to do that with proton therapy. So, x-ray therapy may be the better option for a subset of patients.
When we identify what we believe will be the most appropriate treatment option, of course informed consent is also part of that process for all radiation procedures. The patient has discussed their goals of treatment, the potential risks and side effects, and provides informed consent for radiation of any type.
In terms of cost of therapy, it is true that proton therapy has a larger infrastructure cost. Usually existing treatment buildings are not sized for the hardware that’s required to deliver proton therapy. So typically, an entirely new building is being built, and that certainly adds to the cost versus just putting a machine in an existing building. The hardware itself is currently more expensive than photon-based therapy machines, but also has a longer anticipated life expectancy. So, the upfront costs are high, and although they’ve been decreasing, that is something that differs as well between proton therapy and x-ray therapy.
It’s currently also more resource intensive to plan and deliver proton therapy. There’s a lot more work that goes into developing the most appropriate treatment plan, monitoring it throughout the course of treatment, and insuring that the plan is delivered as good as it looks on paper. Those costs have been reduced to some extent, and we anticipate they will continue to decline with improvements in technology, automation of certain process, and that’s true across all of radiation. Computer learning, and more streamlined technology interfaces can allow us to reduce some of the people power that goes into delivery of radiation therapy.
The cost of delivery of proton therapy certainly varies by the market that you're in, the insurance carrier, the contracts that exist. There are some markets where proton therapy is delivered at cost parity to IMRT, the more fancy type of x-ray therapy. So, it really kind of depends on the market, the treatment plan, the contracts that are in place, and the payor.
Melanie: In what ways are the Emory Proton Therapy Center different than other centers regarding radiation technologies and as part of an academic medical center? Dr. McDonald, how does Winship’s unique position to lead research in clinical trials in proton help as a treatment modality?
Dr. McDonald: Well, we’re tremendously excited to have the Emory Proton Therapy Center open for patient care. We’re also very happy that it’s a fully integrated part of Winship Cancer Institute. Proton therapy may only be a small part of a patient’s treatment plan. We believe that proton therapy is best integrated in the setting of an academic cancer center where the entire patient is being considered. And the patient has access to the resources of Winship, including clinical trials and the latest and greatest technologies of all different types of treatment that might be involved in their care.
We believe that proton therapy is a tremendous resource in the setting of an academic medical center. Because of the way that we’re structured and focused on optimizing the best plan of care for a patient, that we’re not trying to push any particular treatment strategy. Again, proton therapy may or may not be the appropriate option for a certain patient. We’re not thinking about just proton therapy. We’re thinking about holistically what’s the most appropriate care for a patient. We have many resources, and now proton therapy is one of the resources that we have available at Winship. We’ll use it when we believe there’s a clinical benefit for the patient, when it’s perhaps part of the clinical trial. If that’s not the appropriate resource, it’s certainly not the only technology that we have to offer for patients.
Melanie: Wrap it up for us Dr. McDonald with what you would like other providers to know about proton therapy at Emory’s Winship Cancer Institute and when you feel it’s important that they refer.
Dr. McDonald: The Emory Proton Therapy Center is Georgia’s only proton therapy center. We’re part of the Winship Cancer Institute, the only national cancer institute designated comprehensive cancer center in the state of Georgia. It’s a very powerful radiation modality that’s applicable in a wide array of cancer diagnosis. It’s not always intuitive of which patients are immediately appropriate for proton therapy versus other radiation options. So, I think the first step is always consultation with a radiation oncologist. All of our radiation oncologists within Winship Cancer Institute are familiar with proton therapy and all of the other options that are available to patients. So, if there’s ever a question about the most appropriate type of radiation for a patient, a consultation with any of our members in the Winship Radiation Oncology department will help to identify the most appropriate plan of care for patients.
Melanie: Thank you so much Dr. McDonald for joining us today and explaining the differences between these types of radiation therapy and what cancers they might be beneficial for, and when to refer. You're listening to Emory Healthcare Rounds. For more information on proton therapy, please visit emoryhealthcare.org/proton. That’s emoryhealthcare.org/proton. For more information on the latest advances in medicine and oncology, please visit emoryhealthcare.org/referwinship. This is Melanie Cole. Thanks so much for listening.
Melanie Cole, MS (Host): Welcome to Emory Healthcare Rounds. I’m Melanie Cole. Today’s topic is proton therapy versus photon therapy. My guest is Dr. Mark McDonald. He’s the medical director of the Emory Proton Therapy Center. Dr. McDonald tell us a little bit about proton therapy and photon therapy and start with proton. What is it used for and what types of cancers can be treated with proton therapy?
Mark McDonald, MD (Guest): Proton therapy is a type of radiation treatment. It is different from the more commonly used x-ray-based radiation because it uses proton particles to deliver the radiation. The main way that it’s different is that it’s better able to concentrate the radiation in the target and reduce and sometimes eliminate unnecessary radiation to things that aren’t supposed to be receiving it. Both types of radiation are commonly used to treat cancers and some noncancerous tumors, and they're actually both very integral to the practice. I think it’s a false dichotomy to say that it’s proton versus photon. Both types of radiation are very useful in certain circumstances. Our goal as clinicians is always to bring the best treatment to the patient.
It can vary depending on the situation and what we’re trying to treat. Proton therapy is generally used in treatment of curative situations. It’s often used in the treatment of brain tumors, head and neck tumors, many childhood cancers, lung tumors, gastrointestinal tumors. It can be used in a wide array of situations. Again, when we are selecting proton therapy, it’s because we believe there may be a clinical benefit to the patient when we use that technology.
Melanie: Then speak about how the applications of both are different. You mentioned some of the cancers that proton therapy would work for. Tell us a little bit why. What is the application that you would see a need for picking one over the other?
Dr. McDonald: I think brain tumors make a very good explanation of the advantages of the proton therapy. When we treat brain tumors with x-ray therapy, the beam comes in, it treats the tumor, and it continues beyond. Exposing normal brain on the way in and beyond the target to higher doses of radiation than we see with proton therapy. With proton therapy, the radiation comes in and the maximum energy is deposited at the location of the tumor. At which point, the protons stop with no radiation to the brain beyond the tumor.
When we think about tumors that we commonly treat in the brain—meningiomas, pituitary adenomas, schwannomas—a whole variety of non-cancerous tumors where the patient has a long, normal life expectancy, radiation is very effective in the treatment of these tumors. It can have downstream consequences that can show up months, years, decades later. These can be reduced or avoided with proton therapy by reducing the amount of normal brain tissues that’s unnecessarily exposed to radiation. So, it’s certainly a preferred radiation treatment option for many tumors that are in the brain where patients have a good chance of cure and are at risk for long term side effects of radiation.
Melanie: You mentioned the down stream exit dose. Explain a little bit how proton therapy is a little more sensitive to tissue density than photon therapy; and how it would affect tumors at a greater depth. Are the physics of photons what make it a little bit difficult to avoid that exit dose downstream from the target?
Dr. McDonald: The way that protons are different is related to the physical interaction in the body. So, x-rays behave one way and protons behave a different way. The physics to proton therapy, the characteristic is termed the Bragg peak. That refers to the maximum energy being deposited at the depth of the tumor followed by an abrupt drop off in the radiation. So, a sudden rise then an abrupt drop off looking like a peak when you graph it out. This Bragg peak means that the proton therapy stops in the body. After reaching the depth of the target, the radiation stops, not exposing tissues beyond that point to unnecessary radiation.
It is true that proton therapy, like x-ray therapy or photon therapy, is sensitive to many different characteristics of the patient including tissue heterogeneities. So many things are taken into account during the treatment planning process to develop the most accurate treatment plan. All plans have uncertainties. No radiation plan is perfect. In many cases, proton therapy can help us to reduce and sometimes eliminate radiation to things that aren’t supposed to be receiving it. We don’t see radiation toxicities in areas that don’t receive radiation.
Melanie: Where does organ motion play a role in your decision of which radiation treatment to use? Alternation and bone position or lung expansion. Can that effect the target coverage and dose to the surrounding structures, which is what you're saying you're trying to avoid.
Dr. McDonald: Absolutely. So, organ motion is an important parameter applicable in all types of radiation. We need to account for the fact that many times the target is moving. This is particularly true when we’re treating a target in the lung or in the abdomen. These areas tend to move with breathing. We have a number of ways to account for that. With photon therapy, breathing is often less of an issue than with proton therapy. It can be more sensitive. Fortunately, a number of software tools and technical interfaces have allowed us to improve our ability to account for organ motion during respiratory activity.
So, with proton therapy, we can account for this with a variety of planning techniques and a variety of patient techniques, such as breath hold. This allows for the delivery of a proton therapy to a small treatment volume while accounting for the fact that the tumor can move some during the breathing cycle.
Melanie: Speak a little bit about patient selection criteria for this decision. Is informed consent a significant issue? Then also speak about the expense. Does that play a role in this picture? Is proton more highly labor intensive with higher operational costs? Speak about that and how you might adjust that if you're dealing with patients such as children.
Dr. McDonald: So, when we talk about radiation therapy, it always starts with a consultation. Part of the consultation is reviewing the patient’s history. Performing a physical exam, reviewing the images that a patient has done. Then explaining the radiation options and determining the best plan of care in terms of radiation with the patient. Proton therapy is not always the most appropriate option. So, when we select proton therapy, it’s because we believe that there's going to be a clinical benefit.
How do we know then? It’s based on past data that’s been acquired where we understand that a certain dose to a certain structure results in a certain risk of toxicity. We know from past data and models that if we can lower the dose by a certain percentage then we can reduce that risk or, in some cases, eliminate a risk. We’re not always able to do that with proton therapy. So, x-ray therapy may be the better option for a subset of patients.
When we identify what we believe will be the most appropriate treatment option, of course informed consent is also part of that process for all radiation procedures. The patient has discussed their goals of treatment, the potential risks and side effects, and provides informed consent for radiation of any type.
In terms of cost of therapy, it is true that proton therapy has a larger infrastructure cost. Usually existing treatment buildings are not sized for the hardware that’s required to deliver proton therapy. So typically, an entirely new building is being built, and that certainly adds to the cost versus just putting a machine in an existing building. The hardware itself is currently more expensive than photon-based therapy machines, but also has a longer anticipated life expectancy. So, the upfront costs are high, and although they’ve been decreasing, that is something that differs as well between proton therapy and x-ray therapy.
It’s currently also more resource intensive to plan and deliver proton therapy. There’s a lot more work that goes into developing the most appropriate treatment plan, monitoring it throughout the course of treatment, and insuring that the plan is delivered as good as it looks on paper. Those costs have been reduced to some extent, and we anticipate they will continue to decline with improvements in technology, automation of certain process, and that’s true across all of radiation. Computer learning, and more streamlined technology interfaces can allow us to reduce some of the people power that goes into delivery of radiation therapy.
The cost of delivery of proton therapy certainly varies by the market that you're in, the insurance carrier, the contracts that exist. There are some markets where proton therapy is delivered at cost parity to IMRT, the more fancy type of x-ray therapy. So, it really kind of depends on the market, the treatment plan, the contracts that are in place, and the payor.
Melanie: In what ways are the Emory Proton Therapy Center different than other centers regarding radiation technologies and as part of an academic medical center? Dr. McDonald, how does Winship’s unique position to lead research in clinical trials in proton help as a treatment modality?
Dr. McDonald: Well, we’re tremendously excited to have the Emory Proton Therapy Center open for patient care. We’re also very happy that it’s a fully integrated part of Winship Cancer Institute. Proton therapy may only be a small part of a patient’s treatment plan. We believe that proton therapy is best integrated in the setting of an academic cancer center where the entire patient is being considered. And the patient has access to the resources of Winship, including clinical trials and the latest and greatest technologies of all different types of treatment that might be involved in their care.
We believe that proton therapy is a tremendous resource in the setting of an academic medical center. Because of the way that we’re structured and focused on optimizing the best plan of care for a patient, that we’re not trying to push any particular treatment strategy. Again, proton therapy may or may not be the appropriate option for a certain patient. We’re not thinking about just proton therapy. We’re thinking about holistically what’s the most appropriate care for a patient. We have many resources, and now proton therapy is one of the resources that we have available at Winship. We’ll use it when we believe there’s a clinical benefit for the patient, when it’s perhaps part of the clinical trial. If that’s not the appropriate resource, it’s certainly not the only technology that we have to offer for patients.
Melanie: Wrap it up for us Dr. McDonald with what you would like other providers to know about proton therapy at Emory’s Winship Cancer Institute and when you feel it’s important that they refer.
Dr. McDonald: The Emory Proton Therapy Center is Georgia’s only proton therapy center. We’re part of the Winship Cancer Institute, the only national cancer institute designated comprehensive cancer center in the state of Georgia. It’s a very powerful radiation modality that’s applicable in a wide array of cancer diagnosis. It’s not always intuitive of which patients are immediately appropriate for proton therapy versus other radiation options. So, I think the first step is always consultation with a radiation oncologist. All of our radiation oncologists within Winship Cancer Institute are familiar with proton therapy and all of the other options that are available to patients. So, if there’s ever a question about the most appropriate type of radiation for a patient, a consultation with any of our members in the Winship Radiation Oncology department will help to identify the most appropriate plan of care for patients.
Melanie: Thank you so much Dr. McDonald for joining us today and explaining the differences between these types of radiation therapy and what cancers they might be beneficial for, and when to refer. You're listening to Emory Healthcare Rounds. For more information on proton therapy, please visit emoryhealthcare.org/proton. That’s emoryhealthcare.org/proton. For more information on the latest advances in medicine and oncology, please visit emoryhealthcare.org/referwinship. This is Melanie Cole. Thanks so much for listening.