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‘Pencil beam’ proton therapy for pediatric brain tumors may better preserve memory
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Pencil beam scanning proton therapy consistently delivered the lowest amount of radiation to the hippocampus and temporal lobes of pediatric patients with brain tumors compared with two other types of radiotherapy, according to study results presented at European Society for Radiotherapy and Oncology Congress.
By sparing brain structures associated with cognition, pencil beam scanning proton therapy may therefore better protect memory function among these patients.
Alongside surgery and chemotherapy, radiotherapy plays an important role in treating brain tumors in children, but we need to protect children’s developing brains from any unnecessary radiation,” study author Laura Toussaint, PhD student in the department of medical physics at Aarhus University Hospital in Denmark, said in a press release. “The more we learn about how to effectively target brain tumors 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.”
Brain tumors are the second most prevalent type of pediatric cancer, according to Toussaint, who noted that the 5-year survival rate for children diagnosed with brain tumors has risen to 75%.
In the modeling study, Toussaint and colleagues evaluated dose patterns in temporal lobe-sparing radiotherapy plans — including volumetric modulated arc therapy, double scanning proton therapy and pencil beam scanning proton therapy — and predicted memory impairments among 10 anonymized patients with pediatric craniopharyngioma (midline tumor, median clinical target volume of 16 cm3). Researchers reviewed CT/MRI scans, clinical structure sets and clinically delivered double scattering proton therapy plans.
They set a total prescription total dose of 54 Gy, administered through a two-phase sequential boost approach.
The researchers optimized temporal lobe-sparing volumetric modulated arc therapy and pencil beam scanning proton therapy plans to provide the same dose to the clinical target volume, upholding consistent target coverage measures. The volumetric modulated arc therapy plans included three noncoplanar arcs, whereas the pencil beam scanning plans utilized two anterior and one posterior fields.
The researchers used CT/MRI to select 30 brain structures related to cognition, including temporal lobe substructures such as amygdala, hippocampus and entorhinal cortex. They assessed the differences among treatment approaches in the fractions of volume receiving low (V10Gy or V20Gy), intermediate (V30Gy or V40Gy) and high (V50Gy) doses for each brain structure related to cognition. They compared the modalities using a logistic dose-response model and a model correlating left hippocampus V20Gy and delayed verbal memory.
Results showed pencil beam scanning proton therapy delivered lower doses to the temporal lobe than double scattering proton therapy and volumetric modulated arc therapy.
Temporal lobe substructure volumes exposed to all dose levels appeared consistently lower with pencil beam scanning vs. double scattering proton therapy, including from 41% to 0% for the left hippocampus at a dose of V10Gy and from 43% to 24% for the left amygdala at a dose of V40Gy.
For brain structures beyond the temporal lobes, both proton modalities resulted in smaller volumes exposed to low doses compared with volumetric modulated arc therapy. However, intermediate and higher dose levels to ventricular substructures appeared lower with volumetric modulated arc therapy, which researchers attributed to field configurations for both of proton modalities.
In general, decreased doses to the temporal lobes and hippocampus reduced the estimated risks for memory impairment with proton therapy, especially pencil beam scanning proton therapy.
“We have looked at three types of radiotherapy, which all aim to successfully treat brain tumors while doing as little damage to children’s brains as possible,” Toussaint said. “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.” - Jennifer Byrne
Reference:
Toussaint L, et al. Abstract OC-0670. Presented at: ESTRO 38 Conference; April 26-30, 2019; Milan.
Disclosures: HemOnc Today could not confirm the authors’ relevant financial disclosures at the time of reporting.