A Comparative Study of Volumetric Intensity Modulated Arc Therapy Versus Conventional IMRT in Head and Neck Cancer Patients

Background: Intensity-modulated radiation therapy (IMRT) is now the method of choice for the treatment of patients with complex-shaped planning target volumes (PTV) targets, especially when concave targets are close to a larger number of organs-at-risk (OAR) as in patients with advanced head and neck cancer. Patients and Methods: Fifteen patients with advanced head and neck cancers (oropharynx, Nasopharynx, and larynx) were selected for this study. Quantitative evaluation of plans was performed by means of standard Dose-Volume Histogram (DVH). The mean dose, V<95 and V>107 was scored for each PTV. The Dose Homogeneity Index (DHI) describes the uniformity of the dose within the planning target volume and is a ratio of the minimum dose (D99.5%) to the maximum dose (D0.5%). Another measure for the dose homogeneity was the standard deviation (SD) of the PTV doses. For the OAR, the mean dose (D-mean) to the parotid glands was scored, the maximum dose to the spinal cord and brain stem, and the mean dose to the oral cavity and the laryngeal area. Results: The dose homogeneity to PTV1, PTV2 and PTV3 were the same for both RA and IMRT. The number of MU per fraction of 2.2Gy resulted to be MU/frIMRT= 1875.73±402 and MU/frRA=588 ± 122 (31% of MU for IMRT) which is statistically significant difference (p=0.00). For the parotid glands the dose was 2Gy lower with RA plans compared with IMRT. Conclusion: RA is a fast, safe, and accurate technique that uses lower MUs than conventional IMRT. Double arc plans provided better sparing of OAR better than IMRT.