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Particle therapy

Particle therapy

Pencil-beam protons protect memory in children with brain tumours

01 May 2019 Tami Freeman
Treatment plans

Children undergoing radiation therapy for brain tumours are at risk of cognitive impairment, as most tumours are located close to brain substructures associated with memory and thinking. Reducing radiation exposure to structures such as the temporal lobes could help minimize such side effects. Research presented at the ESTRO 38 conference in Milan shows that pencil-beam scanning (PBS) proton therapy delivers the lowest doses of radiation to the temporal lobes and hippocampus — offering the best hope of preserving cognitive function.

“Brain tumours are the second most common type of cancer in children. Survival rates have increased in recent decades and currently 75% of children diagnosed with a brain tumour will be alive five years later,” explains Laura Toussaint, a PhD student at Aarhus University Hospital, who presented the research. “Alongside surgery and chemotherapy, radiotherapy plays an important role in treating brain tumours in children, but we need to protect children’s developing brains from any unnecessary radiation. The more we learn about how to effectively target brain tumours while minimizing the dose to other parts of the brain, the better we can preserve children’s cognitive abilities and quality-of-life after treatment.”

Toussaint and colleagues used data from 10 children with the brain tumour craniopharyngioma. For each child, they created treatment plans using three types of radiotherapy: temporal lobe sparing volumetric-modulated arc therapy (VMAT); double-scattering proton therapy (DSPT); and PBS proton therapy. In each case, the three plans were optimized to deliver the same dose to the clinical target volume.

Previous research has shown that radiation exposure to particular areas of the brain, including the temporal lobes and hippocampus, have an impact on children’s cognitive outcomes, specifically memory functions. Toussaint and colleagues used these existing data to select 30 unique brain substructures associated with cognition to study.

They used CT and MRI scans to precisely delineate the structures in each patient’s brain. For every child, they then compared the three treatment plans see which plan better spared each of the 30 structures from radiation, categorizing the dose to each structure as low (V10Gy, V20Gy), intermediate (V30Gy, V40Gy) or high (V50Gy).

They found that doses to temporal lobe structures were lower with PBS, compared with both the DSPT and VMAT plans. For example, 41% of the left hippocampus volume received low doses of radiation with the DSPT plans, but was spared with PBS. Intermediate dose to the left amygdala was reduced from 43% to 24% for PBS compared with DSPT.

Using existing data and models on the impacts of radiation to these brain regions, the researchers predict that the proton therapies, particularly PBS, would result in less impairment of the children’s memory function.

“We have looked at three types of radiotherapy, which all aim to successfully treat brain tumours while doing as little damage to children’s brains as possible,” says Toussaint. “What we found was that pencil-beam scanning proton therapy seems to be by far the best at avoiding parts of the brain that are important in children’s memory. The next step would be to confirm this finding with clinical research in patients.”

“The aim of radiotherapy is to effectively treat cancer while causing as little damage as possible to the rest of the body. This aim could not be more important than when we are treating children’s brains,” comments Umberto Ricardi, President of ESTRO and head of the University of Turin’s oncology department. “Proton therapy is already being used in some hospitals to treat brain tumours in children, but this study offers evidence of the benefits it might bring in terms of protecting cognitive functions and quality-of-life. We hope this work will lead to more research in this vital area.”

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