Dosimetric comparison of intensity-modulated radiation therapy and volumetric-modulated arc therapy plans for the treatment of glioma using flattening filter-free and flattening filter modes

In the present study, the dose verification between 6X and 6X flattening filter-free (FFF) in intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) was compared, and the advantages and disadvantages of different radiotherapy plans were evaluated. All four plans achieved comparable heterogeneity and conformity indices. For frontal tumor, VMAT demonstrated more improved sparing of the brainstem compared with the IMRT (P=0.045); while in the model of FFF, the Dmax of eye lens was significantly reduced by 16-21% (P<0.001). The organs at risk (OARs) in the temporal lobe tumor were spared well in the IMRT plan. With the removal of FF, the low-dose volume for both tumor locations was significantly reduced (P<0.05). By contrast, there was no significant difference in monitor units (MUs) with FFF, but the MUs were significantly reduced in the VMAT plan (P<0.001). Regarding the protection of OARs, FFF appeared to be superior compared with FF. For the frontal glioma, the VMAT plan had more advantages, and for temporal lobe tumor, dynamic IMRT was more appropriate. The VMAT plan reduces the low-dose volume of normal brain tissues and the MUs. While the removal of FF may increase the dose rate, the shortened treatment delivery time may improve the accuracy of treatment due to intra-fractional patient motion.