Intensity-modulated proton therapy decreases dose to organs at risk in low-grade glioma patients: results of a multicentric <i>in silico</i> ROCOCO trial

<b>Background and purpose:</b> Patients with low-grade glioma (LGG) have a prolonged survival expectancy due to better discriminative tumor classification and multimodal treatment. Consequently, long-term treatment toxicity gains importance. Contemporary radiotherapy techniques such as intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), tomotherapy (TOMO) and intensity-modulated proton therapy (IMPT) enable high-dose irradiation of the target but they differ regarding delivered dose to organs at risk (OARs). The aim of this comparative <i>in silico</i> study was to determine these dosimetric differences in delivered doses. <b>Material and methods:</b> Imaging datasets of 25 LGG patients having undergone postoperative radiotherapy were included. For each of these patients, <i>in silico</i> treatment plans to a total dose of 50.4 Gy to the target volume were generated for the four treatment modalities investigated (i.e., IMRT, VMAT, TOMO, IMPT). Resulting treatment plans were analyzed regarding dose to target and surrounding OARs comparing IMRT, TOMO and IMPT to VMAT. <b>Results:</b> In total, 100 treatment plans (four per patient) were analyzed. Compared to VMAT, the IMPT mean dose (<i>D</i>_mean) for nine out of 10 (90%) OARs was statistically significantly (<i>p</i> <b>Discussion:</b> The low dose volume to the majority of OARs was significantly reduced when using IMPT compared to VMAT. Whether this will lead to a significant reduction in neurocognitive decline and improved quality of life is to be determined in carefully designed future clinical trials.