Temporal lobe sparing radiotherapy with photons or protons for cognitive function preservation in paediatric craniopharyngioma

BACKGROUND AND PURPOSE:

Reducing radiation exposure to the temporal lobes could be beneficial to preserve cognitive function in paediatric brain tumour patients. The distribution of doses to brain substructures associated with cognition (BSCs) both within and outside of the temporal lobe have not been reported. The aim of this study was therefore to investigate temporal lobe sparing photon vs. proton therapy for paediatric suprasellar tumours.

MATERIAL AND METHODS:

Data from ten anonymized craniopharyngioma patients were used in this study. Temporal lobe sparing volumetric modulated arc therapy (VMAT) and pencil beam scanning (PBS) proton therapy plans were optimized to maintain consistent target metrics as in the delivered double scattering proton therapy (DSPT) plans. Thirty BSCs were delineated, including temporal lobe substructures (i.e. amygdala, hippocampus, entorhinal cortex). The dose/volume fractions to each BSC were analysed, and intelligence quotient (IQ) as well as memory scores were estimated to compare the different modalities.

RESULTS:

The exposed volumes of the temporal lobes and their substructures were consistently reduced with PBS compared to DSPT and VMAT, e.g. the left hippocampus V10Gy from 100% (VMAT) or 41% (DSPT) to 5% with PBS (p = 0.002). Some of the ventricular substructures were better spared with VMAT compared to both proton modalities. The reduced doses to the temporal lobes achieved with PBS translated into improved predicted memory outcomes, but not for the estimated IQ.

CONCLUSION:

The irradiated volumes of temporal lobe BSCs were consistently the lowest with PBS, whereas the model-based estimates of cognitive outcomes were less consistent.