Advances in Proton Therapy - Pencil Beam

M. D. Anderson Cancer Center
Cancer Newsline Audio Podcast Series
Date: March 30, 2009
Duration: 0 / 20:05

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Edward Kim, M.D.:

Welcome to Cancer Newsline, a weekly podcast series from the University of Texas M. D. Anderson Cancer Center. Cancer Newsline helps you stay current with all the news on cancer research, diagnosis, treatment and prevention providing the latest information on reducing your families’ cancer risk. I’m your host, Dr. Edward Kim assistant professor in the department of Thoracic Head and Neck Medical Oncology.

Today we are talking about proton therapy with Dr. James Cox, professor and head of the division of Radiation Oncology at M. D. Anderson and Dr. Andrew Lee, associate professor and the director of M. D. Anderson’s Proton Therapy Center. The Proton Therapy Center at M. D. Anderson is the largest and most sophisticated facility of its kind in the world. Proton therapy derives its advantage over traditional form of radiation treatment from its ability to deliver radiation doses to a targeted tumor with remarkable precision – within one millimeter. That avoids the surrounding tissue, generates few side effects and improves tumor control. The twin goals of controlling disease and minimizing side effects are the aims of radiation treatment and protons enhance the opportunity for both.

Thanks very much to both of you for joining us today and Dr. Cox, or Jim as I’ll call you, why don’t we start with you. Can you offer our listeners a little background regarding proton therapy, how it works and what are the real benefits over traditional radiation therapy?

James Cox, M.D.:

Proton therapy in many ways is very similar to x-ray treatments – which is what we give everyday all over the world. But, protons allow for the ability to concentrate the dose just where the tumor is and avoid the tissues around it – especially on the other side of the tumor because the protons deposit their dose in the tumor and then they simply stop. There is no radiation beyond that and it’s just one of the ways with the distribution of the dose that we can avoid the normal tissues. So, as you said our goal is to avoid normal tissues which lets us avoid side effects and if we can do that, we can also increase the dose where the tumor is and we can have both a higher dose in the tumor and fewer side effects which is a great situation.

Dr. Kim:

And clearly more radiation to the tumor means better outcomes for the patient.

Dr. Cox:

Right, better control.

Dr. Kim:

Now, I know that M. D. Anderson has been treating patients since 2006. I remembered when this proton facility opened and everybody was very eagerly anticipating having their patients treated. Since then I know that a lot of other facilities across the country have come open or there are plans to build proton centers. Can you comment on just what this growing trend is and how the need is going to change in the future for proton?

Dr. Cox:

There’s interest in at least a substantial part of the radiation oncology community to have proton therapy more widely available and the centers that are planned will hopefully let us expand the experience that we’ve had, expand our indications and work with us in many ways to accomplish things that centers working together can do. There is a lot of interest and we think a lot of that is targeted at certain diseases and perhaps the wide range of diseases that we’re interested in exploring. And so that makes us different at least in principle from most of the other facilities around the nation.

Dr. Kim:

I know you all are very selective, I’ve been pushing to get head and neck cancer patients of my own treated with proton, but I know it takes time to do that.

Dr. Cox:

We will get there!

Dr. Kim:

So obviously Jim, and you’ve overseen this program for many years, you all have really sat on the forefront of radiation oncology. What is M. D. Anderson going to do in the next decade to try and advance this field?

Dr. Cox:

The main thing that we are going to do is try to expand the indications for proton therapy, which really requires a great deal of work. With the new pencil beam which you will hear about, with better utilization of the tools that we have, both treatment planning tools and the actual delivery. So, I think that’s our main goal.

Dr. Kim:

That’s wonderful and I hope to be sending you many patients over for further indications. Dr. Lee, or Andy, I know your area or focus is prostate cancer. Can you talk a little bit about the proton therapy’s history in treating prostate cancer and how it offers something different and unique for these patients?

Andrew K. Lee, M.D.:

Sure Ed.  Actually in the United States, prostate cancer has probably been the most common disease treated with proton therapy.  Certainly one of the earlier experiences involved prostate cancer and proton therapy performed at the Harvard Cyclotron in Boston Massachusetts or actually in Cambridge, and from a clinical based proton facility standpoint, Loma Linda has extensive experience and has a long history of treating prostate cancer with proton therapy, and that’s part of the reason why proton therapy is so good for prostate cancer is that it tends to be a deep seated tumor and the adjacent tissue around it can be sensitive to radiation.  That includes the bladder as well as the rectum.  The unique properties of proton therapy as Dr. Cox alluded to basically can maximize the dose to the tumor which is typically in the prostate and minimize the dose to the adjacent tissue – specifically the rectum and bladder.

Dr. Kim:

That’s very interesting, and I know the original patients who are treated here were first prostate cancer patients who came. I believe that’s correct?

Dr. Lee:

That’s correct. The first patient treated on May 4, 2006 in fact was a prostate cancer patient. Subsequently, the patient tolerated therapy quite well and at the last follow up he was also doing quite well. Probably one of the reasons why prostate cancer is one of the more common disease sites treated with proton therapy is that there is just a lot of it. In the US, the annual incidence of prostate cancer is quite prevalent and it’s increasing.

Dr. Kim:

It’s nice to hear that the patient is doing well since that first opening. So Andy, tell me why a patient should come here, particularly to M. D. Anderson and seek out proton therapy from one of the experts like yourself.

Dr. Lee:

That’s a good question, Ed. Although proton therapy is available at other centers, it is somewhat limited. One of the things that I think we provide at M. D. Anderson is patient focused care. Although I primarily treat with proton therapy these days, I’d like to think of myself as sort of dedicated to being a prostate cancer specialist first and utilizing proton therapy as a tool to cure prostate cancer. More importantly is that when you come to the M. D. Anderson Proton Therapy Center, you’re not just getting the Proton Therapy Center benefits; you’re getting the benefits of M. D. Anderson. We have a. I think multidisciplinary team here that’s able to take care of patients more fully than perhaps just going to an isolated proton therapy treatment center. So, leveraging the resources and the expertise of M. D. Anderson as a whole I think makes a big difference. We also provide some unique technologies here that are not widely available, such as the pencil beam scanning. That’s a unique technology where right now there’s only two centers in all of North America that are able to treat with pencil beam scanning and I believe there’s only four Proton Therapy centers available worldwide. That number may change, but that is a unique tool we have at our hands to help patients and decrease the possibility of side effects while at the same time maximizing their cure rates.

Dr. Kim:

Clearly this seems something so sophisticated that experience can only help as you continue to plan for patients.

Dr. Lee:

Absolutely. Although proton therapy has been in existence for over a decade in this country, we’re making great strides just in the past few years to improve the delivery and optimizing proton therapy. 

Dr. Kim:

So tell me about this new technology, pencil beam, and how it offers more precision than traditional therapy.

Dr. Lee:

Sure Ed. Well, about 99 percent of proton therapy in the world has been delivered using what’s called passive scattered or conventional proton therapy. Pencil beam scanning offers another way to deliver the protons in a more precise manner. Probably the closest analogy is if you think about protons like you would paint. The physical properties of paint when it’s sitting in a bucket are all about the same, but that paint can be delivered to a wall in a different manner. You can use a brush, you can use a spray can. So conventional, or passive scattered protons, basically is like using a can of spray paint to cover whatever target you need. Now, we want to be more precise than just spraying protons all over the place, so we typically use brass blocks to customize the proton dose in the proton beams so it covers just the area we’re interested in covering. But that requires a certain amount of effort in order to make that hardware. Now, if you take pencil beam scanning, the analogy would be instead of a can of spray paint, you’d basically have a fine detailed airbrush. Because you are able to deposit the dose in a very precise manner, you don’t need that brass block anymore. Typically what we’ll do is we’ll spray for a given tumor one spot and move over, spray another spot, move over, and spray another spot and so on and so on. But, as you know, tumors are three dimensional targets and so we typically have to treat multiple layers. So, we may start with the deepest layer first and move superficially. For Example, typical prostate may be anywhere from 18 to 2000 spots, but because of the sophisticated technology, we’re able to deliver all those spots in a matter of a couple of minutes.

Dr. Kim:

So is this something I get to start calling you about and bugging you about sending some of my patients to as well, both head and neck and lung?

Dr. Lee:

Eventually, I think right now we’re starting with one disease site, typically in the pelvis. But we’re hoping to expand the indications to more complicated disease sites. One of the areas we’re very keen on utilizing this technology is in cancers of the skull base as well as the head and neck for brain tumors and for complicated tumors involving the spine. And of course, I think we ultimately would like to treat larger fields and it could have a big benefit, especially in pediatric malignancies.

Dr. Kim:

That’s fascinating stuff! So Jim, as you know we’ve worked together, I see lung cancer patients. We like to believe, and I believe that lung cancer is an exciting area for proton therapy research. Tell me how you’ve been able to use it, how your experience has been using it at the same time or concurrently with chemotherapy and what you’re seeing in these patients.

Dr. Cox:

Well, as you know Ed, we combine chemotherapy and radiation therapy together at the same time in a large proportion of patients with so called non-small cell carcinoma of the lung. And that’s our sort of standard of care. What we are doing with the proton treatment is similar combining the proton therapy with chemotherapy. But what we are learning is that because we can leave out structures that cause discomfort during treatment; for example, leave out the esophagus so people don’t have discomfort in swallowing. And leave out a lot of normal lung so the risk of treatment related pneumonia which is one of the most serious side effects of this treatment can be reduced to almost nothing. So, we’re very excited about that. 

Dr. Kim:

Jim, I know you all have been very busy in lung cancer trying to develop clinical trials. I’ve had the pleasure of participating in a few of them. Can you give us an overview on what’s available and what are we trying to study? 

Dr. Cox:

We have the opportunity to use more than one type of advanced technology in the care of patients with cancer of the lungs – especially those that are getting chemotherapy with the radiation therapy at the same time. And so, IMRT was a big step forward - Intensity Modulated Radiation Therapy – which was a way of focusing x-ray treatments to a smaller area and avoiding normal tissues. We’ve done so well with that and now as I mentioned earlier we’ve done this also with the proton therapy. We’re going to try to figure out with the help of our patients who are our collaborators in this regard, we’re going to try to find out which is better. They are both better than anything we’ve ever done. Which of them is better? We are going to have a clinical trial that is going to compare proton therapy and IMRT, with a lot of advanced techniques of imaging and image guidance and so on for both of them

Dr. Kim:

My understanding is the outcome could be that the conclusion is that they are both equally as good, but proton may be better as far as side effects and more same for the patient. 

Dr. Cox:

That’s quite possible, and the side effects are one of the parts that we are going to study. We have an endpoint of trying to improve control the tumor, but we also have as an endpoint to try and reduce the side effects in the patients. 

Dr. Kim:

Clearly in this curative population maybe the best goal of the study is to lessen the side effects.

Dr. Cox:

Actually, you touched on something very important. The patients that we’re treating with proton therapy, and of course with IMRT in this particular trial, we are treating with curative intent. This is a treatment that is designed to try to increase the cure rate in patients with cancer - of all the kinds that we treat. So that’s a very important distinction.

Dr. Kim:

Clearly when we talk about prostate cancer, we are treating all those people for cures and you get to see those patients for long term, Andy, but in lung cancer, our options have been looked upon more in a pessimistic tone, but I think something like proton certainly lends some optimism that we can try and improve the cure rates. Dr. Cox, exactly! You know, many of the patients that I encounter, as I talk to them about different options for therapy, including surgery or radiotherapy, many of them know that it’s important to find a surgeon who has vast experience in exposure to a field. They don’t have that same understanding about a radiotherapist and Dr. Cox, for our listeners, can you tell us what’s so important about having experience in the delivering and planning of radio therapy and not just finding a center that does for instance that does IMRT or other technologies. 

Dr. Cox:

One of the most important aspects of care at M. D. Anderson is the fact that we have teams of people who can concentrate on a particular disease. This is very true in radiation therapy and it’s true as a part of the proton center. We have a team of expert physicists, dosimetrists, therapist, the people who actually see the patients everyday at the machine, the physician, all of these people work together and they in general are taking care of only one set of diseases. So Andy is concentrating on cancer of the prostate, I’m concentrating on cancer of the lung, and our respective teams are supporting us in this way. So, with the analogy that you suggested with this surgeon who has vast experience and has treated hundreds or thousands of patients with a particular type of cancer, the same kind of expertise develops with the radiation oncologist in his or her team.

Dr. Kim:

I think that’s something that not many patients realize, that this is not just like getting a CAT scan, it really is planning and development. So finally, and Jim, you’ve got to be very proud of what you’ve build here and what you’ve seen over time. The future of proton therapy here at M. D. Anderson, what are the top two goals you want to see?

Dr. Cox:

Well, one of the goals is to expand the use of the pencil beam to these other disease sites where we need the finesse of being able to paint the beam in critical areas and we have a lot of work to do in this area. Dr. Lee is leading it. We have other people who have expertise in head and neck that want to develop it also, so that is one of the major thrusts. The other one I think is building on what we have already started, which is combining proton therapy and chemotherapy together for a variety of diseases. Because the normal structures, avoid the side effects, we can give higher doses, we can spare the bone marrow better with the proton therapy, so there is just a lot of opportunity to improve on what we do. 

Dr. Kim:

I want to thank you both, Dr. Cox and Dr. Lee. We’ve had a very nice discussion today and I hope our listeners have benefited from this information. 

If you have any question about anything you have heard today on Cancer Newsline, contact askmdanderson at 1-877-MDA-6789 or online at www.mdanderson.org/ask. Thank you for listening to this episode of Cancer Newsline. Tune in next week for the next podcast in our series.

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