A dosimetric comparison of volumetric modulated arc therapy (VMAT) and non-coplanar intensity modulated radiotherapy (IMRT) for nasal cavity and paranasal sinus cancer.

Yuri Jeong,Jungwon Kwak,Seung Do Ahn,Ji Hyeon Joo,Su Ssan Kim,Jong Hoon Kim,Sang-Wook Lee,Jin-Hong Park,Ilsung Cho,Sang Min Yoon,Young Seok Kim,Si Yeol Song,Eun Kyung Choi

doi:10.1186/1748-717x-9-193

Abstract

BackgroundTo compare dosimetric parameters of volumetric modulated arc therapy (VMAT) and non-coplanar intensity modulated radiotherapy (IMRT) 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).MethodsTen patients with nasal cavity or paranasal sinus cancer were re-planned by VMAT (two-arc) plan and non-coplanar IMRT (7-, 11-, and 15-beam) plans. Planning objectives were to deliver 60 Gy in 30 fractions to 95% of PTV, with maximum doses (Dmax) of <50 Gy to the optic nerves, optic chiasm, and brainstem, <40 Gy to the eyes and <10 Gy to the lenses. The target mean dose (Dmean) to the parotid glands was <25 Gy, and no constraints were applied to the lacrimal glands. Planning was optimized to minimized doses to OAR without compromising coverage of the PTV. VMAT and three non-coplanar IMRT (7-, 11-, and 15-beam) plans were compared using the heterogeneity and conformity indices (HI and CI) of the PTV, Dmax and Dmean of the OAR, treatment delivery time, and monitor units (MUs).ResultsThe HI and CI of VMAT plan were superior to those of the 7-, 11-, and 15-beam non-coplanar IMRT. VMAT and non-coplanar IMRT (7-, 11-, and 15-beam) showed equivalent sparing effects for the optic nerves, optic chiasm, brainstem, and parotid glands. For the eyes and lenses, VMAT achieved equivalent or better sparing effects when compared with the non-coplanar IMRT plans. VMAT showed lower MUs and reduced treatment delivery time when compared with non-coplanar IMRT.ConclusionsIn 10 patients with nasal cavity or paranasal sinus cancer, a VMAT plan provided better homogeneity and conformity for PTV than non-coplanar IMRT plans, with a shorter treatment delivery time, while achieving equal or better OAR-sparing effects and using fewer MUs.

Highlights

To compare dosimetric parameters of volumetric modulated arc therapy (VMAT) and non-coplanar intensity modulated radiotherapy (IMRT) 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)
Planning target volume coverage The heterogeneity index (HI) and conformity index (CI) of VMAT and each of the 7, 11, and 15-beam non-coplanar IMRT plans for each of the 10 patients are shown in Figures 1 and 2
The CI was superior in VMAT plans compared with each of 7, 11, 15-beam non-coplanar IMRT plans (Table 2)

Summary

Introduction

To compare dosimetric parameters of volumetric modulated arc therapy (VMAT) and non-coplanar intensity modulated radiotherapy (IMRT) 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). Standard treatment for locally advanced nasal cavity and paranasal sinus cancer is surgery followed by postoperative radiotherapy, or definitive radiotherapy with or without chemotherapy. Intensitymodulated radiotherapy (IMRT) can provide more conformal dose coverage for the target volume, with reduced dosage to the adjacent critical organs, when compared with two- or three-dimensional radiotherapy [3,4,5,6,7]. Non-coplanar beams may provide additional optimization capacity within inverse planning processes for the target volumes of the nasal cavity and paranasal sinus cancer, which are usually located between both eyes. VMAT may reduce treatment delivery time with lower monitor units (MUs) while providing conformal dose distribution [8,9,10,11]

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Conclusion