RapidArc vs Conventional IMRT for Head and Neck Cancer Irradiation: Is Faster Necessary Better?

PURPOSE: The aim of this study was to dosimetrically evaluate and compare double arc RapidArc (RA) with conventional IMRT (7 fields) plans for irradiation of locally advanced head and neck cancers (LAHNC), focusing on target coverage and doses received by organs at risk (OAR). METHODS: Computed tomography scans of 20 patients with LAHNC were obtained. Contouring of the target volumes and OAR was done. Two plans were made for each patient, one using IMRT and the other double arc RA, and calculated doses to planning target volume (PTV) and OAR were compared. Monitor units for each technique were also calculated. RESULTS: PTV coverage was similar with both techniques. The homogeneity index (HI) was higher for the IMRT plans with a value of 0.108 ± 0.021 compared to 0.0975 ± 0.017 for double arc RA plans (p-value of 0.540). The double arc RA plans achieved a better conformity with a CI95%= 1.01 ± 0.021 compared to 1.05 ± 0.057 achieved with the IMRT plans (p-value of 0.036). The average monitor units (MU) ±SD were 930.5 ± 142.42 for the IMRT plans as opposed to 484.25 ± 69.47 for the double arc RA plans (P-value of 0.002). Double arc plans provided better OAR sparing with a significant p-value of 0.002 and 0.004 for the right and left parotid glands, respectively. CONCLUSIONS: RA is a rapid and accurate technique that uses lower MUs than conventional IMRT. Double arc plans provide better dose conformity, OAR sparing and a more homogeneous target coverage compared to IMRT.