Comparison of RapidArc and Static Gantry Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

Objective: RapidArc (Varian Medical Systems, Palo Alto, CA) is a new volumetric-modulated arc radiotherapy technique with continuous modulation of gantry speed, dose rate, and multileaf collimator shape. Taking advantages of dose painting capabilities along with rotational delivery, RapidArc has shown promise in the treatment of a wide range of tumours, including intracranial, head and neck, prostate, and endometrial cancers. However, supportive data on RapidArc therapy for nasopharyngeal carcinoma are scanty. In this study, comparison of the quality of a treatment plan and efficiency of radiation delivery by RapidArc and intensitymodulated radiotherapy for nasopharyngeal carcinoma was evaluated. Methods: Datasets of 3 nasopharyngeal carcinoma patients were used to design both RapidArc and intensitymodulated radiotherapy plans. Results were analysed in terms of dose distribution and dose-volume histograms. Results: For all patients, RapidArc plans provided a comparable homogeneity index and adequate organs-atrisk sparing relative to intensity-modulated radiotherapy plans. In terms of target dose conformity, the conformity index favoured intensity-modulated radiotherapy, especially for higher dose targets using a simultaneous integrated boost approach. Conclusion: Taken together, our preliminary experience in dose optimisation with RapidArc for radiation treatment of nasopharyngeal carcinoma was able to deliver reasonable treatment plans. Development of a sophisticated planning system with a quick optimisation algorithm and adjustable level of modulation appears crucial to take full advantage of RapidArc technology. With the ever-increasing complexity of RapidArc treatment planning and delivery, further parallel efforts in optimising quality assurance are warranted.