Dosimetric comparison of intensity-modulated proton therapy and photon-based radiotherapy for skull base tumors

To compare dosimetric differences between intensity-modulated proton therapy (IMPT) and photon-based radiotherapy (VMAT/IMRT) in the treatment of skull base tumors, focusing on target coverage and organ-at-risk (OAR) sparing.

All patients with skull base tumors who underwent proton therapy between December 2021 and August 2022 were included in this study. For each case, both IMPT and VMAT/IMRT plans were generated using Eclipse TPS, with robust optimization applied for protons. Dosimetric metrics for target volumes and OARs-including the brainstem, spinal cord, visual pathways, eyes, lenses, and salivary glands-were extracted and compared. Key endpoints included $D_{2\%}$ , $D_{\text{mean}}$ , conformity index (CI), and homogeneity index (HI). Statistical comparisons were performed using non-parametric Wilcoxon signed-rank tests, with significance set at p<0.05.

Target coverage was comparable between IMPT and photon plans ( $D_{98\%}$ of 57.51 $\pm$ 6.14 Gy for photon and 58.06 $\pm$ 5.85 Gy for proton, p = 0.12, respectively). IMPT provided statistically significant dose reductions to brainstem, spinal cord, lenses, eyes, and the right parotid. The brainstem $D_{2\%}$ was reduced from 45.70 $\pm$ 11.49 Gy of photons to 39.47 $\pm$ 13.03 Gy of protons (p = 0.037). Dose reductions of $\sim$ 29%-83% were observed for other above OARs. Although no significant difference was found in doses to the left parotid or visual pathways, substantial dose reductions were observed in individual cases.

IMPT achieved equivalent target coverage to VMAT/IMRT while offering superior sparing of several critical OARs. These findings support the clinical potential of IMPT in the management of anatomically complex skull base tumors, particularly when normal tissue preservation is a key concern.