SU-E-T-302: Dosimetric Comparison Between Volumetric Modulated Arc Radiotherapy and Intensity-Modulated Radiotherapy for Locally Recurrent Nasopharyngeal Carcinoma

Purpose: To compare volumetric modulated arc radiotherapy (VMAT) technique with fixed-gantry intensity-modulated radiotherapy (IMRT) technique for locally recurrent nasopharyngeal carcinoma. Methods: CT datasets of eleven nasopharyngeal-carcinoma patients were included. Dual-arc VMAT and seven-field IMRT plans were created for each case, and were then compared in terms of conformity index (CI), homogeneity index (HI) of the planning target volume (PTV), organ-at-risk (OAR) sparing, monitor unit (MU) and delivery time. Results: The D98% (near-minimal dose) of PTV in the VMAT plans was slightly lower than that of the IMRT plans (P < 0.05), while the CI was higher than that of the IMRT plans (P < 0.05). No significant difference was found in the HI between the two plans (P > 0.05). Compared with the IMRT plans, the VMAT plans demonstrated lower Dmean (mean dose) of the bilateral temporal lobes and the whole surrounding normal tissue (P < 0.05), but slightly higher Dmean of brainstem (P < 0.05). In terms of the other OARs, no significant differences were found (P > 0.05). The MUs of the VMAT plans (672 ± 112) was significantly lower than that of the IMRT plans (917 ± 206), by 25 ± 13% (P < 0.05). The average delivery time of the VMAT plans (2.3 ± 0.1 min) was less than that of the IMRT plans (5.1 ± 0.4 min), by 54 ± 3%. Conclusion: For locally recurrent nasopharyngeal carcinoma, the VMAT technique could achieve equivalent or superior dose distribution of the target and better protect the bilateral temporal lobes, compared with the IMRT technique. Moreover, it could reduce the MU and delivery time effectively.