Clinical relevance of the radiation dose bath in lower grade glioma, a cross-sectional pilot study on neurocognitive and radiological outcome.

Aim: To investigate the clinical relevance of the radiotherapy (RT) dose bath in patients treated for lower grade glioma (LGG). Methods: Patients (n = 17) treated with RT for LGG were assessed with neurocognitive function (NCF) tests and structural Magnetic Resonance Imaging (MRI) and categorized in subgroups based on tumour lateralisation. RT dose, volumetric results and cerebral microbleed (CMB) number were extracted for contralateral cerebrum, contralateral hippocampus, and cerebellum. The RT clinical target volume (CTV) was included in the analysis as a surrogate for focal tumour and other treatment effects. The relationships between RT dose, CTV, NCF and radiological outcome were analysed per subgroup. Results: The subgroup with left-sided tumours (n = 10) performed significantly lower on verbal tests. The RT dose to the right cerebrum, as well as CTV, were related to poorer performance on tests for processing speed, attention, and visuospatial abilities, and more CMB.In the subgroup with right-sided tumours (n = 7), RT dose in the left cerebrum was related to lower verbal memory performance, (immediate and delayed recall, r = -0.821, p = 0.023 and r = -0.937, p = 0.002, respectively), and RT dose to the left hippocampus was related to hippocampal volume (r = -0.857, p = 0.014), without correlation between CTV and NCF. Conclusion: By using a novel approach, we were able to investigate the clinical relevance of the RT dose bath in patients with LGG more specifically. We used combined MRI-derived and NCF outcome measures to assess radiation-induced brain damage, and observed potential RT effects on the left-sided brain resulting in lower verbal memory performance and hippocampus volume.