SMARTARC-BASED VOLUMETRIC MODULATED ARC THERAPY FOR OROPHARYNGEAL CANCER: A DOSIMETRIC COMPARISON WITH BOTH INTENSITY-MODULATED RADIATION THERAPY AND HELICAL TOMOTHERAPY

Purpose: To investigate the roles of volumetric modulated arc therapy with Smart Arc (VMAT-S), intensity-modulated radiation therapy (IMRT), and helical tomotherapy (HT) for oropharyngeal cancer using a simultaneous integrated boost (SIB) approach. Methods and Materials: Eight patients treated with IMRT were selected at random. Plans were computed for both IMRT and VMAT-S (using Pinnacle TPS for an Elekta Infinity linac) along with HT. A three-dose level prescription was used to deliver 70 Gy, 63 Gy, and 58.1 Gy to regions of macroscopic, microscopic high-risk, and microscopic low-risk disease, respectively. All doses were given in 35 fractions. Comparisons were performed on dose volume histogram data, monitor units per fraction (MU/fx), and delivery time. Results: VMAT-S target coverage was close to that achieved by IMRT, but inferior to HT. The conformity and homogeneity within the PTV were improved for HT over all strategies. Sparing of the organs at risk (OAR) was achieved with all modalities. VMAT-S (along with HT) shortened delivery time (mean, -38%) and reduced MU/fx (mean, -28%) compared with IMRT. Conclusion: VMAT-S represents an attractive solution because of the shorter delivery time and the lower number of MU/fx compared with IMRT. However, in this complex clinical setting, current VMAT-S does not appear to provide any distinct advantage compared with helical tomotherapy. (C) 2011 Elsevier Inc.