The Dosimetric Comparison of Step-and-Shoot Intensity Modulated Radiotherapy and Helical Tomotherapy in Nasopharyngeal Carcinoma

Abstract

Purposes: The purpose of this study was to demonstrate the benefit in dosimetric gaining of intensity-modulated radiotherapy (IMRT) between step-and-shoot IMRT (SaS-IMRT) and helical tomotherapy (HT) in nasopharyngeal carcinoma (NPC) of the same patient contouring data. Materials and methods: A retrospective study of fifty-two patients, histologic confirm diagnosed NPC stage I-IVb, treated by SaS-IMRT (Konrad version 2.2.23 SP2), were included and re-planned by HT (HiArt version 4.2.1). The conformity index (CI), homogeneity index (HI), Conformity improvement ratio (ΔCI%), homogeneity improvement ratio (ΔHI%) of planning target volume of 70 Gy (PTV70) for tumor target volume and quality index (QI) of the organ at risks (OARs) between the two techniques were compared. Results: The study revealed the significant improvement of CI and HI with the improvement ratio 1.21% ± 3.35 (p=0.015) and 9.20% ± 2.82 (p<0.001), respectively, in HT planning over SaS-IMRT planning. Besides, the reduction in the mean values of max/mean doses of the OARs except the optic apparatus. However, the maximum doses of the optic apparatus were not exceeding the maximum organs tolerance. The beam on time in HT plans were significant shorter compared with SaS-IMRT. Conclusion: In conclusion, the HT plan showed significant better CI and more homogeneous over SaS-IMRT in NPC patients with the tolerable doses to the OARs.