Radiotherapy for maxillary sinus carcinoma: dosimetric comparison of volumetric modulated arc therapy with 0° and 90° collimator intensity modulated radiation therapy

To compare volumetric modulated arc therapy (VMAT) with 0° and 90° collimator intensity modulated radiation therapy (IMRT) plans for treatment of maxillary sinus carcinomas (MSCs). Eighteen MSC were re-planned for VMAT (two full arcs), 0° collimator 9 beams IMRT (zc-IMRT) and 2 beams with 90° collimator and the remaining 7 beams with 0° collimator IMRT (nc-IMRT). The conformity and homogeneity index (CI and HI) of target volume, dose-volume histogram (DVH) of organs at risk (OARs), and monitor units (MUs) were analyzed. The CI of VMAT with GTV, PTV,1 and PTV2 found significantly more than zc-IMRT and nc-IMRT. The HI of nc-IMRT found significantly smaller than VMAT. In terms of OARs, VMAT significantly reduced the maximum point dose of optic chiasm, the ipsilateral lens, MUs, and the D1% of the ipsilateral lens compared with IMRT. VMAT significantly reduced the maximum point dose of ipsilateral optic nerve, the D1% of optic chiasm, the ipsilateral optic nerve and the mean dose of contralateral eyeball compared with zc-IMRT. For the two IMRT group plans, comparison with zc-IMRT, nc-IMRT could significantly reduce the maximum point dose of ipsilateral lens, the D1% of ipsilateral lens and the MUs. The VMAT has better CI of target volume and could have better OARs sparing effects for optic chiasm, ipsilateral lens and ipsilateral optic nerve compared with IMRT for MSCs. The VMAT also could use fewer MUs and has lower treatment delivery times. The nc-IMRT could have better ipsilateral lens sparing and use fewer MUs compared with zc-IMRT. Therefore we could protect the ipsilateral lens better through changing the angle of the collimator from 0° to 90° when the IMRT technique is used for the treatment of MSCs.