Low-grade gliomas (LGGs) are the most common brain tumors in children, and a subset of these tumors are treated definitively with focal radiation therapy (RT). These patients often survive for many years after receiving RT and experience late deficits in memory. Verbal recall is an important measure of memory and is associated with other important functional outcomes, such as problem-solving, independence of every-day functioning, and quality of life. Decline in memory, as measured by verbal recall, is associated with RT dose to the hippocampi. Therefore, this phase II study investigates the feasibility of reducing RT doses to the hippocampi (i.e., hippocampal avoidance \[HA\]) by using proton therapy for midline or suprasellar LGGs. Primary Objective: * To determine the feasibility of HA with proton therapy in suprasellar or midline LGGs. Feasibility will be established if 70% of plans meet the first or second dose constraints shown below. 1. First priority RT dose constraints for bilateral hippocampi: volume receiving 40 CGE (V40CGE) ≤ 25%, dose to 100% of Hippocampus (D100%) ≤ 5CGE. 2. Second priority RT dose constraints for bilateral hippocampi: V40CGE ≤ 35%, D100% ≤ 10 CGE. Secondary Objectives: * To estimate the 3-year event-free-survival (EFS) for LGGs treated with HA. * To estimate the change in California Verbal Learning Test short-term delay (CVLT-SD) from baseline to 3 years and from baseline to 5 years * To compare CVLT-SD and Cogstate neurocognitive scores in patients with proton therapy plans that: (1) meet first priority RT dose constraints, (2) meet second priority RT dose constraints but not first priority RT dose constraints, and (3) that did not meet either first or second RT priority dose constraints Exploratory Objectives: * To describe the change in overall cognitive performance from baseline to 3 years and from baseline to 5 years with an age appropriate battery, including gold standard measures shown in the published studies to be sensitive to attention, memory processing speed and executive function that will afford comparison to historical controls. * To characterize longitudinal changes in connection strength within brain networks in the first 3 years after proton therapy and to investigate associations between these changes and neurocognitive performance with focus on the hippocampi. * To correlate the distribution and change in L-methyl-11C-methionine positron emission tomography (MET-PET) uptake to tumor progression and from baseline to 3 years and to investigate whether cases of pseudoprogression exhibit a differential pattern of uptake and distribution compared to cases of true progression after controlling for histology. * To investigate the effect of BRAF alteration, tumor histology and tumor location on PFS and OS in a prospective cohort of patients treated in a homogenous manner. * To investigate whether the methylation profiles of LGGs differ by tumor location (thalamic/midbrain vs. hypothalamic/optic pathway vs. others) and histologies (pilocytic astrocytoma vs. diffuse astrocytoma vs. others), which, in conjunction with specific genetic alterations, may stratify patients into different subgroups and highlight different therapeutic targets. * To record longitudinal measures of circulating tumor DNA (ctDNA) in plasma and correlate these measures with radiographic evidence of disease progression. * To bank formalin-fixed, paraffin-embedded (FFPE)/frozen tumors and whole blood from subjects for subsequent biology studies not currently defined in this protocol. * To quantify and characterize tumor infiltrating lymphocytes (TILs) and to characterize the epigenetics of T cells and the T cell receptor repertoire within the tumor microenvironment. * To estimate the cumulative incidence of endocrine deficiencies, vision loss, hearing loss and vasculopathy after proton therapy and compare these data to those after photon therapy.
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Percentage of plans meet the first or second dose constraints.
Timeframe: 4 years after activation