ASTRO 2015
Does photon radiation therapy reduce ear toxicity in children with medulloblastoma?
Dr Arnold Paulino - MD Anderson Cancer Centre, Houston, USA
We’ve been looking at medulloblastoma, it’s one of the most common brain tumours in children and it’s typically treated with radiation therapy where we give radiation therapy to the whole brain and the entire spine. Part of the problem with treating the brain is that we’re also getting the hearing apparatus, mainly the cochlea, when we do radiation. But aside from radiation therapy these patients are also getting cisplatin chemotherapy which also causes ototoxicity. So the project that we presented today is looking at the effect of proton radiation therapy on hearing loss, primarily grade 3 or 4 hearing loss in these patients.
So what we did was we compared patients who were treated with photons which is the more traditional way that we have treated medulloblastoma. We know that in these patients there are about 20% grade 3-4 ototoxicity. Based on some preliminary data that we had from four years ago at our centre we were getting about 5% ototoxicity, grade 3 or 4 ototoxicity, in these patients but when we followed these patients longer we found the same amount of ototoxicity which is about 20%.
How old were the children you studied?
The median age of the children was eight years and predominantly more than two-thirds of the patients were male, which is representative of this tumour because most patients with this tumour are male.
What is unique about the study, was cisplatin used in all children?
Cisplatin is not really unique because that’s part of the traditional treatment. What is unique about this research is the comparison between protons and photons. When we treat with protons we always think that we can do better as far as preservation of hearing and actually in our study we found that the cochlea, which is the inner ear, is getting less radiation dose. But despite the fact that they’re getting less radiation dose, because they’re still getting the cisplatin chemotherapy the hearing loss is the same. So even if we lower the radiation dose to the inner ear they still get the same grade 3 or 4 ototoxicity.
Do you have to give the chemotherapy?
The implication is if you wanted to preserve more hearing maybe find other agents, other chemotherapy agents that don’t have the hearing toxicity. Or maybe if they can use a lower dose but it’s something for investigation in the future.
What about the use of immunotherapies?
Immunotherapy, I am not sure how that would cause less late toxicity. But right now the way that medulloblastoma is treated is you get a molecular profile and based on the molecular profile your radiation might be different. So some patients are actually getting a lower radiation dose now but these are studies that people are doing in Europe and also here in North America.
What is the main result of the study?
The main result is that the grade 3 or 4 hearing loss is the same whether you use cochlear sparing proton or photon radiotherapy and it’s because of the cisplatin chemotherapy. So we can lower the dose of radiation but after a certain point it doesn’t really matter because you are still giving the chemotherapy that causes hearing loss.
The next step will be if were concerned about hearing loss then find ways, find different agents, that are effective as far as chemotherapy that doesn’t cause hearing loss. Or if there is a lower dose of the drug that can be used that’s also as effective.
