Session Item

Radiotherapy-induced neurocognitive decline affects 50-90% of adult glioma survivors. Several organs at risk (OARs) have been identified to play a role in neurocognitive functioning. Proton therapy is expected to outperform photon therapy in sparing many of these OARs from excess dose. In this study, we compared Volumetric Modulated Arc Therapy (VMAT) vs Intensity Modulated Proton Therapy (IMPT) for its OAR sparing capability in glioma patients.

In this in silico dosimetric comparison study, we included 10 glioma patients (grade II and III astrocytoma and oligodendroglioma) who were treated to a total dose of 54-60 GyRBE. Seven tumours were located in the left hemisphere, two in the right hemisphere and one in the brainstem. The OARs that could play a role in neurocognitive functioning (cerebellum anterior and posterior, ipsi- and contralateral thalamus, ipsi- and contralateral hippocampus, corpus callosum, supratentorial brain minus CTV, brain (minus CTV))  were delineated according to the EPTN atlas for contouring in neuro-oncology¹. For each patient, both a VMAT (2 partial arcs) and robust IMPT (2-3 beams) treatment plan were optimized according to the same set of clinical dose constraints. Average and near-maximum (D2%) doses in 9 OARs were extracted from the planning system (Raystation and Eclipse). To evaluate the dose metrics of the IMPT plan, the nominal scenario was used. To evaluate target coverage, D95% of the CTV was used in both treatment techniques. DVH metrics from both techniques were compared using a two-sided Wilcoxon rank-sum test with a p-value of <0,05 indicating significance.

In total, 20 treatment plans were analysed (1 VMAT and 1 IMPT for each patient). A statistically significant reduction was established using IMPT in 6 out of 21 dose metrics in 3 out of 5 OARs important in neurocognitive functioning: Dmean supratentorial brain minus CTV (p<0,001), Dmean contralateral hippocampus (p=0,019), D40% contralateral hippocampus (p=0,001), Dmean brain (p=0,007), Dmean brain minus CTV (p< 0,001) and Dmean contralateral thalamus (p=0,002). The dose coverage (D95% CTV) was not statistically different between both groups (p=0,529).

The use of IMPT resulted in important OAR sparing in this glioma patient population translating in a lower mean dose to the contralateral hippocampus, contralateral thalamus and supratentorial brain minus CTV, and a lower D40% to the contralateral hippocampus. To evaluate whether this translates into a clinical benefit for these patients, we will compare the ROCOCO Performance Scoring System scores² between both groups in a planned analysis.