Proton Therapy Treatment for Brain Tumors

MD Anderson Cancer Center
Date: 10-31-2011

 

Lisa Garvin: Welcome to Cancer Newsline, a podcast series from the University of Texas M.D. Anderson Cancer Center. Cancer Newsline helps you stay current with the news on cancer research, diagnosis, treatment, and prevention providing the latest information on reducing your family's cancer risk. I'm your host Lisa Garvin. Today, we're taking with Dr. Paul Brown who is the co-chief of Central Nervous System in Pediatrics Radiation Oncology here at M.D. Anderson and our subject today is proton therapy treatment for adult brain cancers. Dr. Brown, what are the most common types of brain cancers you've been treating with proton therapy?

Paul Brown, MD: There's a large variety of brain tumors and we treat a minority of brain tumors with protons. The ones we tend to treat and has a strong indication are for those cases when we have to treat the whole spine and the brain, a phrase or term that's often used as craniospinal irradiation, CSI is another phrase that's used. When a tumor indicates that type of treatment, the craniospinal treatment, there's a huge benefit for protons compared to standard radiation or photon radiation therapy and there's a reason for that. We've talked before in this podcast where protons will deposit the radiation to the depth where we want them to deposit. That's a big difference between photons when the radiation keeps going through, so there's radiation being deposited throughout its whole course, throughout the whole body and it's a big advantage for protons in those situations. And to give you an example when treating the spine there'll be no dose to the intestines, the lungs, to the heart and that's just so beneficial for our patients, the young adults and the older patients getting craniospinal access.

Lisa Garvin: Typically, we think of treatment for brain cancer, brain tumors being surgery, so is proton kind of a departure from the standard treatment?

Paul Brown, MD: Often, these patients will still get surgery. The tumors just [inaudible] often require craniospinal irradiation. They're unusual tumors, but we do see them in our practice. There'd be tumors such as medulloblastoma, a tumor you think about typically associated with kids, but you do see it in adults, not infrequently; pinealblastoma, pineal parenchymal tumors, more aggressive pineal parenchymal tumors. Those types of tumors are tumors where you have to worry about small tumor cells going throughout the spinal canal and that's why we have to treat the spine and the brain, and that's why the huge advantages for craniospinal irradiation. I think about, in some of my past experiences when I didn't have protons available and I treat adults with standard radiation, photon radiation and the toxicity is almost unbearable for these patients. Kids can tolerate craniospinal irradiation with photons much better than adults. Adults can barely even tolerate it, so it is very hard on them. You contrast that to my experience using protons and it's night and day. The toxicity is so much less. During a treatment an expected much less toxicity long term for the 10, 20, 30, 40, 50-years going forward.

Lisa Garvin: And plus there are fewer treatments with proton as opposed to photon?

Paul Brown, MD: We often use the same number of treatments and there's a reason for that, that's a good point. There's a reason why we often use the same number of treatments is by using the same number of treatments is we're gently delivering the radiation therapy. So for example, with photons we often treat the brain and the spine in 20 treatments, we'll do the same with protons and again it just be very gentle with the normal tissues.

Lisa Garvin: Are you using pencil beam with CNS tumors?

Paul Brown, MD: We are, yeah, so, and we're starting to use that more and more in certain cases. There's some cases where there is an advantage, where that's often a big advantage for tumors with irregular shapes, we often have a big advantage with the pencil beam. And we're developing new techniques, they're not quite ready for primetime but techniques such as one called Intensity Modulated Proton Therapy or IMPT. I won't go into too many specifics on that, but it is basically using some of the techniques delivered with normal radiation, photon radiation, uses similar same techniques using that in the proton world. So, IMPT is something we're very interested in.

Lisa Garvin: And let's describe both pencil beam and IMRT. Pencil beam is--explain.

Paul Brown, MD: Yeah. So, I'll start with normal radiation, photon radiation doing IMRT and then we'll do pencil beam start that way.

Lisa Garvin: Okay, sounds good and IMRT standing for Intensity Modulated Radiation Therapy.

Paul Brown, MD: That's exactly right. So, the I way I think of IMRT is you're modifying the intensity of the beam throughout the beam itself, so you have the capabilities of within multiple beams, but just taking one beam, you can adjust the intensity. So, maybe the top part of the beam, you want to have a third of the intensity as the bottom part of the beam you can have double, three times intensity and you can fine tune it even more than that. Pencil beam is starting to get us more towards that direction with protons and that's the direction we want to go. Eventually, we want to be doing the same type of techniques with IMRT with protons, in other words, IMPT.

Lisa Garvin: Now, where does proton therapy fall in the treatment spectrum? You say often these patients do need surgery, is its adjuvant therapy so is happening before or after the surgery or does it depend on the case?

Paul Brown, MD: It depends on the case, but for the vast majority it's after the surgery. That would be typical for I would say 90-percent plus of our patients.

Lisa Garvin: And medulloblastomas as you mentioned tends to be an adolescent and young adult disease, how many of your patients have been like under the age of 25 that you've treated with proton therapy?

Paul Brown, MD: Yeah, it's not uncommon that we are seeing young adults with these tumors and we're much, we are interested in all adults with these certain select tumors treating with protons, but just because they're so common in these young adults that's often why we see these patients with young patients, the medulloblastomas. Another one I didn't mentioned was one called PNET, P-N-E-T, primitive neuroectodermal tumor. That's another common tumor we'll see in young adults where again, that's an indication for craniospinal irradiation.

Lisa Garvin: What are the indications as far as long term effects especially for young people whose brains may still have some development left, have you had enough critical data to determine whether it's more efficacious?

Paul Brown, MD: Where the benefit for the craniospinal access or craniospinal irradiation cases, the biggest benefit is the absence of radiation to those anterior structures and it's actually, it's huge, it's huge during the treatment, the tolerance, but also long term. So, they're going to have much less risk of damage to the heart, to the lungs, much less risk of second malignancy such cancers in the thyroid gland and other tissues, much less risk of damage to the intestines, so the list really goes on and on. So, that's where your benefit is dramatic for these long term survivors. And you'll see those toxicities in patients who get the standard radiation, the photon radiation and the risk is so, so much less. It's almost zero for a lot of those cases because of the proton, so it's just really little dose I guess to those anterior structures.

Lisa Garvin: Our Proton Therapy Center opened in 2006, have you been able to treat very many CNS tumors with protons?

Paul Brown, MD: Yeah and our practice is growing in that. It remains a minority of the CNS adult tumors, so there's select cases where we tend to use, will there be advantage for protons. We tend to basically pick the ones where we think there should be a key advantage for these patients. So, examples for that would be some of the meningeomas, we see a benign tumor, some of the large acoustic schwannomas, cases like that where we think there is going to be a dramatic advantage for protons. For the majority of the brain tumors we see, we're still treating with photon just because there may not be a big difference between the two, but yeah, our practice is growing for adult brain tumors.

Lisa Garvin: Now, as far as treatment simulation for proton, I mean, and a lot of people may not know this, there's actually a frame that's built, you know, in the treatment simulation, so the patient is in the exact same position every time. Is the treatment simulation the same for protons as is it for photons?

Paul Brown, MD: It's very similar, yeah. There's very little difference between the two. It's a soft plastic mask that typically forms around the face. It's warm when it goes on and then it hardens to form to the face. Myself being a little bit claustrophobic, I always like to try out the mask and see what they're like. They are not bad even for someone who is mildly claustrophobic like myself, but they're very similar between proton and photon, with just some very minor differences.

Lisa Garvin: Where do you see proton therapy treatment going for other tumors? I don't know glioblastomas are kind of difficult, do you foresee proton being expanded to a wide range of brain tumors?

Paul Brown, MD: I do, it's a great question. I think where there could be huge potential is for some of the lower grade tumors, the grade twos, the grade threes, if we could show that there is a advantage long term from a cognitive or thinking ability, and the reason where photons whenever advantages you can decrease the amount of dose to the surrounding brain. You just can't do that as well with standard radiation therapy. So, I can see happening in the future is us designing trials to look at that question and if we can prove that, I think that would really open the door for those patients.

Lisa Garvin: And proton has been a big buzz word for other diseases such as prostate cancer and lymphoma. Do you find that people are cognizant of the fact that proton therapy may be an option to treat brain tumors?

Paul Brown, MD: They are, but not to the--you're right, they are but not to the degree of say prostate or something like that. So, we are getting contacted by people normally individually, not necessarily through the doctor, but people individually contacting the Proton Center and then we fill those calls, but it is not out there to the degree of prostate cancer for example as you mentioned.

Lisa Garvin: What would be and we talked about this a little bit earlier off mic, not every brain tumor would be a good candidate for proton therapy, what would be kind of the perfect patient for proton therapy?

Paul Brown, MD: Yeah, perfect patient would be generally at this point would be benign tumors and there's a reason for that is the advantage of proton is the dose falls off so rapidly and that's a good thing. You are decreasing the amount of radiation to the surrounding brain, but benign tumors are very sharply demarcated. There's not tumor cells extended beyond them, so that's why protons works well for those. We'd mentioned earlier glioblastoma, we don't treat those tumors with protons and there's reason for that, there have tumor cells that's spread out from them and that's way kind of lose the advantage of that sharp border with protons compared to the standard photon radiation therapy.

Lisa Garvin: And you talked a little bit about some new things you're trying without like giving away the bank, what kind of avenues are you looking at to hone brain cancer treatment with protons?

Paul Brown, MD: Yeah, so a study or trial that were planning to open in conjunction with MGH Boston group is looking at IMPT increasing the dose or dose escalation study for patients with the benign tumor called chordoma. That's actually one of the most established indications for protons and that is one that's well recognized in the community if a person develops a chordoma or a chondrosarcoma. Those people do tend to know that they should be receiving proton radiotherapy, so they will come to our facility or other proton facilities. So, our goal with this trial is to improve our results with IMPT, increase the dose and decrease any risk of long term side effects.

Lisa Garvin: Great. Anything else on the horizon?

Paul Brown, MD: I'd mentioned some other studies that there'll be a couple of years down the road looking at things such as the neurocognitive endpoints with protons compared to photons, but the IMPT one for chordomas and chondrosarcomas, that we should be open to that trial soon.

Lisa Garvin: I think it's very exciting, I mean, you know, when we opened our Proton Therapy, it was one of only a handful of centers in the nation. It must be exiting to have something that's so new and that you've been able to make so many advances in in such a short time.

Paul Brown, MD: Yeah. We're fortunate to come in when we did here at M.D. Anderson with the Proton Center and you make a good point there, we're seeing a lot of centers now being developed. I think that gives us a lot of opportunities for collaborative research going forward. Cancers are some of these difficult questions.

Lisa Garvin: In a nutshell or if you had to say something to somebody who had a brain tumor that might be amendable to proton therapy treatment, what would you tell them to do?

Paul Brown, MD: Yeah, the first thing is just to contact the Proton Center. We're always building questions and that's what we're here for, we're here to help sort through who'd be a good candidate for protons and who would not be. It's hard to make that decision without the proper training and we're more than willing to do that and we normally have pretty quick turn around on our answers.

Lisa Garvin: Great. Thank you very much for being with us today.

Paul Brown, MD : Thank you.

Lisa Garvin: If you have questions about anything you've 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 for the next podcast in our series.

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