Acta oncologica
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Background: Proton arc therapy may improve physical dose conformity and reduce concerns of elevated linear energy transfer (LET) and relative biological effectiveness (RBE) at the end of the proton range, while offering more degrees of freedom for normal tissue sparing. To explore the potential of proton arc therapy, we studied the effect of increasing the number of beams on physical and biologically equivalent dose conformity in the setting of pediatric brain tumors. Material and methods: A cylindrical phantom (Ø = 150 mm) with central cylindrical targets (Ø = 25 and 30 mm) was planned with increasing number of equiangular coplanar proton beams (from 3 to 36). ⋯ Overall, the temporal lobes were better spared with the sagittal proton arc surrogate plans, e.g. a mean dose of 3.9 Gy compared to 6 Gy in the reference 3-beam plan (median value, RBE1.1). Conclusion: Proton arc therapy has the potential to improve dose gradients to better spare cognitive brain structures. However, this is at the expense of increased low-dose/low-LET volumes, with possible implications for secondary cancer risks.