Investigating variation of dose gradient index by different grid sizes in intensity-modulated radiation therapy of optic nerve sheath meningioma.

In optic nerve sheath meningioma (ONSM) radiotherapy, vital organs with a low tolerance dose are very close to the target volume. Thus dose fall-off steepness around the target volume is the most critical parameter in intensity-modulated radiation therapy (IMRT) planning for this malignancy. We hypothesized that one of the parameters that can impact the dose fall-off steepness is dose calculation grid sizes. This study aimed to assess the impact of different dose calculation grid sizes on the newly introduced dose gradient indices (DGIs) for the steepness of dose fall-off around the target volume. Results showed that decreasing the dose calculation grid size in IMRT treatment planning of ONSM patients had a significant difference in the dosimetric parameters and DGIs of the target volume and at-risk organs. This study demonstrates that using a finer dose calculation grid size is preferred in treating ONSM patients.