Dosimetric Study Of Two Radiotherapy Planning For Postoperative Nasal Cavity And Paranasal Sinuses Cancer

Objective:To compare dosimetric parameters of VMAT(two-arc)and IMRT(9-beam)for nasal cavity and paranasal sinus cancer with regard to the coverage of planning target volume(PTV) and the sparing of organs at risk(OAR).Materials and methods:Eight patients with nasal cavity and paranasal sinus cancer were re-planned by VMAT(two-arc) plan and IMRT(9-beam) plan. Planning objectives were to deliver 50 Gy in 25 fractions to 95% of PTV, with maximum dose of <54Gy to the optic nerve, optic chisam, and brainstem, <50Gy to the eyes and <9Gy to the lens. VMAT(two-arc) plan and IMRT(9-beam) plan were compared using the heterogeneity and conformity indices(HI and CI), Dmean, D95 and D5 of the PTV, Dmax and Dmean of the OAR, treatment delivery time, and monitor units(MUs).Results:(1)The HI and CI of VMAT(two-arc) plan were superior to those of IMRT(9-beam) plan.(2) Protection of organs at risk: VMAT(two-arc) was better than IMRT(9-beam) in the protection of eyes, brainstem and optic chiasm(P<0.05).Compared with IMRT(9-beam), VMAT(two-arc)’s Dmax of optic nerve, brainstem, optic chisam and lens was little lower, while Dmean of optic nerve was higher, but the differences were not statistically significant.(3) VMAT showed lower Mus and reduced treatment delivery time when compared with IMRT.Conclusion:In early stage nasal cavity and paranasal sinus cancer, a VMAT plan provided better heterogeneity and conformity of PTV than IMRT, with a shorter treatment delivery time, while achieving equal or better OAR-sparing effects and using fewer MUs, therefore, for nasal cavity and paranasal sinus cancer postoperative radiotherapy planning choice, VMAT(two-arc) technology in modern precision treatment mode has obvious advantages.